what is research hypothesis definition

What Is A Research (Scientific) Hypothesis? A plain-language explainer + examples

By:  Derek Jansen (MBA)  | Reviewed By: Dr Eunice Rautenbach | June 2020

If you’re new to the world of research, or it’s your first time writing a dissertation or thesis, you’re probably noticing that the words “research hypothesis” and “scientific hypothesis” are used quite a bit, and you’re wondering what they mean in a research context .

“Hypothesis” is one of those words that people use loosely, thinking they understand what it means. However, it has a very specific meaning within academic research. So, it’s important to understand the exact meaning before you start hypothesizing. 

Research Hypothesis 101

• What is a hypothesis ?
• What is a research hypothesis (scientific hypothesis)?
• Requirements for a research hypothesis
• Definition of a research hypothesis
• The null hypothesis

What is a hypothesis?

Let’s start with the general definition of a hypothesis (not a research hypothesis or scientific hypothesis), according to the Cambridge Dictionary:

Hypothesis: an idea or explanation for something that is based on known facts but has not yet been proved.

In other words, it’s a statement that provides an explanation for why or how something works, based on facts (or some reasonable assumptions), but that has not yet been specifically tested . For example, a hypothesis might look something like this:

Hypothesis: sleep impacts academic performance.

This statement predicts that academic performance will be influenced by the amount and/or quality of sleep a student engages in – sounds reasonable, right? It’s based on reasonable assumptions , underpinned by what we currently know about sleep and health (from the existing literature). So, loosely speaking, we could call it a hypothesis, at least by the dictionary definition.

But that’s not good enough…

Unfortunately, that’s not quite sophisticated enough to describe a research hypothesis (also sometimes called a scientific hypothesis), and it wouldn’t be acceptable in a dissertation, thesis or research paper . In the world of academic research, a statement needs a few more criteria to constitute a true research hypothesis .

What is a research hypothesis?

A research hypothesis (also called a scientific hypothesis) is a statement about the expected outcome of a study (for example, a dissertation or thesis). To constitute a quality hypothesis, the statement needs to have three attributes – specificity , clarity and testability .

Let’s take a look at these more closely.

Need a helping hand?

Hypothesis Essential #1: Specificity & Clarity

A good research hypothesis needs to be extremely clear and articulate about both what’ s being assessed (who or what variables are involved ) and the expected outcome (for example, a difference between groups, a relationship between variables, etc.).

Let’s stick with our sleepy students example and look at how this statement could be more specific and clear.

Hypothesis: Students who sleep at least 8 hours per night will, on average, achieve higher grades in standardised tests than students who sleep less than 8 hours a night.

As you can see, the statement is very specific as it identifies the variables involved (sleep hours and test grades), the parties involved (two groups of students), as well as the predicted relationship type (a positive relationship). There’s no ambiguity or uncertainty about who or what is involved in the statement, and the expected outcome is clear.

Contrast that to the original hypothesis we looked at – “Sleep impacts academic performance” – and you can see the difference. “Sleep” and “academic performance” are both comparatively vague , and there’s no indication of what the expected relationship direction is (more sleep or less sleep). As you can see, specificity and clarity are key.

Hypothesis Essential #2: Testability (Provability)

A statement must be testable to qualify as a research hypothesis. In other words, there needs to be a way to prove (or disprove) the statement. If it’s not testable, it’s not a hypothesis – simple as that.

For example, consider the hypothesis we mentioned earlier:

Hypothesis: Students who sleep at least 8 hours per night will, on average, achieve higher grades in standardised tests than students who sleep less than 8 hours a night.  

We could test this statement by undertaking a quantitative study involving two groups of students, one that gets 8 or more hours of sleep per night for a fixed period, and one that gets less. We could then compare the standardised test results for both groups to see if there’s a statistically significant difference. 

Again, if you compare this to the original hypothesis we looked at – “Sleep impacts academic performance” – you can see that it would be quite difficult to test that statement, primarily because it isn’t specific enough. How much sleep? By who? What type of academic performance?

So, remember the mantra – if you can’t test it, it’s not a hypothesis 🙂

Defining A Research Hypothesis

You’re still with us? Great! Let’s recap and pin down a clear definition of a hypothesis.

A research hypothesis (or scientific hypothesis) is a statement about an expected relationship between variables, or explanation of an occurrence, that is clear, specific and testable.

So, when you write up hypotheses for your dissertation or thesis, make sure that they meet all these criteria. If you do, you’ll not only have rock-solid hypotheses but you’ll also ensure a clear focus for your entire research project.

What about the null hypothesis?

You may have also heard the terms null hypothesis , alternative hypothesis, or H-zero thrown around. At a simple level, the null hypothesis is the counter-proposal to the original hypothesis.

For example, if the hypothesis predicts that there is a relationship between two variables (for example, sleep and academic performance), the null hypothesis would predict that there is no relationship between those variables.

At a more technical level, the null hypothesis proposes that no statistical significance exists in a set of given observations and that any differences are due to chance alone.

And there you have it – hypotheses in a nutshell. 

If you have any questions, be sure to leave a comment below and we’ll do our best to help you. If you need hands-on help developing and testing your hypotheses, consider our private coaching service , where we hold your hand through the research journey.

Psst... there’s more!

This post was based on one of our popular Research Bootcamps . If you're working on a research project, you'll definitely want to check this out ...

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16 Comments

Very useful information. I benefit more from getting more information in this regard.

Very great insight,educative and informative. Please give meet deep critics on many research data of public international Law like human rights, environment, natural resources, law of the sea etc

In a book I read a distinction is made between null, research, and alternative hypothesis. As far as I understand, alternative and research hypotheses are the same. Can you please elaborate? Best Afshin

This is a self explanatory, easy going site. I will recommend this to my friends and colleagues.

Very good definition. How can I cite your definition in my thesis? Thank you. Is nul hypothesis compulsory in a research?

It’s a counter-proposal to be proven as a rejection

Please what is the difference between alternate hypothesis and research hypothesis?

It is a very good explanation. However, it limits hypotheses to statistically tasteable ideas. What about for qualitative researches or other researches that involve quantitative data that don’t need statistical tests?

In qualitative research, one typically uses propositions, not hypotheses.

could you please elaborate it more

I’ve benefited greatly from these notes, thank you.

This is very helpful

well articulated ideas are presented here, thank you for being reliable sources of information

Excellent. Thanks for being clear and sound about the research methodology and hypothesis (quantitative research)

I have only a simple question regarding the null hypothesis. – Is the null hypothesis (Ho) known as the reversible hypothesis of the alternative hypothesis (H1? – How to test it in academic research?

this is very important note help me much more

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The Craft of Writing a Strong Hypothesis

Table of Contents

Writing a hypothesis is one of the essential elements of a scientific research paper. It needs to be to the point, clearly communicating what your research is trying to accomplish. A blurry, drawn-out, or complexly-structured hypothesis can confuse your readers. Or worse, the editor and peer reviewers.

A captivating hypothesis is not too intricate. This blog will take you through the process so that, by the end of it, you have a better idea of how to convey your research paper's intent in just one sentence.

What is a Hypothesis?

The first step in your scientific endeavor, a hypothesis, is a strong, concise statement that forms the basis of your research. It is not the same as a thesis statement , which is a brief summary of your research paper .

The sole purpose of a hypothesis is to predict your paper's findings, data, and conclusion. It comes from a place of curiosity and intuition . When you write a hypothesis, you're essentially making an educated guess based on scientific prejudices and evidence, which is further proven or disproven through the scientific method.

The reason for undertaking research is to observe a specific phenomenon. A hypothesis, therefore, lays out what the said phenomenon is. And it does so through two variables, an independent and dependent variable.

The independent variable is the cause behind the observation, while the dependent variable is the effect of the cause. A good example of this is “mixing red and blue forms purple.” In this hypothesis, mixing red and blue is the independent variable as you're combining the two colors at your own will. The formation of purple is the dependent variable as, in this case, it is conditional to the independent variable.

Different Types of Hypotheses‌

Types of hypotheses

Some would stand by the notion that there are only two types of hypotheses: a Null hypothesis and an Alternative hypothesis. While that may have some truth to it, it would be better to fully distinguish the most common forms as these terms come up so often, which might leave you out of context.

Apart from Null and Alternative, there are Complex, Simple, Directional, Non-Directional, Statistical, and Associative and casual hypotheses. They don't necessarily have to be exclusive, as one hypothesis can tick many boxes, but knowing the distinctions between them will make it easier for you to construct your own.

1. Null hypothesis

A null hypothesis proposes no relationship between two variables. Denoted by H 0 , it is a negative statement like “Attending physiotherapy sessions does not affect athletes' on-field performance.” Here, the author claims physiotherapy sessions have no effect on on-field performances. Even if there is, it's only a coincidence.

2. Alternative hypothesis

Considered to be the opposite of a null hypothesis, an alternative hypothesis is donated as H1 or Ha. It explicitly states that the dependent variable affects the independent variable. A good  alternative hypothesis example is “Attending physiotherapy sessions improves athletes' on-field performance.” or “Water evaporates at 100 °C. ” The alternative hypothesis further branches into directional and non-directional.

• Directional hypothesis: A hypothesis that states the result would be either positive or negative is called directional hypothesis. It accompanies H1 with either the ‘<' or ‘>' sign.
• Non-directional hypothesis: A non-directional hypothesis only claims an effect on the dependent variable. It does not clarify whether the result would be positive or negative. The sign for a non-directional hypothesis is ‘≠.'

3. Simple hypothesis

A simple hypothesis is a statement made to reflect the relation between exactly two variables. One independent and one dependent. Consider the example, “Smoking is a prominent cause of lung cancer." The dependent variable, lung cancer, is dependent on the independent variable, smoking.

4. Complex hypothesis

In contrast to a simple hypothesis, a complex hypothesis implies the relationship between multiple independent and dependent variables. For instance, “Individuals who eat more fruits tend to have higher immunity, lesser cholesterol, and high metabolism.” The independent variable is eating more fruits, while the dependent variables are higher immunity, lesser cholesterol, and high metabolism.

5. Associative and casual hypothesis

Associative and casual hypotheses don't exhibit how many variables there will be. They define the relationship between the variables. In an associative hypothesis, changing any one variable, dependent or independent, affects others. In a casual hypothesis, the independent variable directly affects the dependent.

6. Empirical hypothesis

Also referred to as the working hypothesis, an empirical hypothesis claims a theory's validation via experiments and observation. This way, the statement appears justifiable and different from a wild guess.

Say, the hypothesis is “Women who take iron tablets face a lesser risk of anemia than those who take vitamin B12.” This is an example of an empirical hypothesis where the researcher  the statement after assessing a group of women who take iron tablets and charting the findings.

7. Statistical hypothesis

The point of a statistical hypothesis is to test an already existing hypothesis by studying a population sample. Hypothesis like “44% of the Indian population belong in the age group of 22-27.” leverage evidence to prove or disprove a particular statement.

Characteristics of a Good Hypothesis

Writing a hypothesis is essential as it can make or break your research for you. That includes your chances of getting published in a journal. So when you're designing one, keep an eye out for these pointers:

• A research hypothesis has to be simple yet clear to look justifiable enough.
• It has to be testable — your research would be rendered pointless if too far-fetched into reality or limited by technology.
• It has to be precise about the results —what you are trying to do and achieve through it should come out in your hypothesis.
• A research hypothesis should be self-explanatory, leaving no doubt in the reader's mind.
• If you are developing a relational hypothesis, you need to include the variables and establish an appropriate relationship among them.
• A hypothesis must keep and reflect the scope for further investigations and experiments.

Separating a Hypothesis from a Prediction

Outside of academia, hypothesis and prediction are often used interchangeably. In research writing, this is not only confusing but also incorrect. And although a hypothesis and prediction are guesses at their core, there are many differences between them.

A hypothesis is an educated guess or even a testable prediction validated through research. It aims to analyze the gathered evidence and facts to define a relationship between variables and put forth a logical explanation behind the nature of events.

Predictions are assumptions or expected outcomes made without any backing evidence. They are more fictionally inclined regardless of where they originate from.

For this reason, a hypothesis holds much more weight than a prediction. It sticks to the scientific method rather than pure guesswork. "Planets revolve around the Sun." is an example of a hypothesis as it is previous knowledge and observed trends. Additionally, we can test it through the scientific method.

Whereas "COVID-19 will be eradicated by 2030." is a prediction. Even though it results from past trends, we can't prove or disprove it. So, the only way this gets validated is to wait and watch if COVID-19 cases end by 2030.

Finally, How to Write a Hypothesis

Quick tips on writing a hypothesis

1.  Be clear about your research question

A hypothesis should instantly address the research question or the problem statement. To do so, you need to ask a question. Understand the constraints of your undertaken research topic and then formulate a simple and topic-centric problem. Only after that can you develop a hypothesis and further test for evidence.

2. Carry out a recce

Once you have your research's foundation laid out, it would be best to conduct preliminary research. Go through previous theories, academic papers, data, and experiments before you start curating your research hypothesis. It will give you an idea of your hypothesis's viability or originality.

Making use of references from relevant research papers helps draft a good research hypothesis. SciSpace Discover offers a repository of over 270 million research papers to browse through and gain a deeper understanding of related studies on a particular topic. Additionally, you can use SciSpace Copilot , your AI research assistant, for reading any lengthy research paper and getting a more summarized context of it. A hypothesis can be formed after evaluating many such summarized research papers. Copilot also offers explanations for theories and equations, explains paper in simplified version, allows you to highlight any text in the paper or clip math equations and tables and provides a deeper, clear understanding of what is being said. This can improve the hypothesis by helping you identify potential research gaps.

3. Create a 3-dimensional hypothesis

Variables are an essential part of any reasonable hypothesis. So, identify your independent and dependent variable(s) and form a correlation between them. The ideal way to do this is to write the hypothetical assumption in the ‘if-then' form. If you use this form, make sure that you state the predefined relationship between the variables.

In another way, you can choose to present your hypothesis as a comparison between two variables. Here, you must specify the difference you expect to observe in the results.

4. Write the first draft

Now that everything is in place, it's time to write your hypothesis. For starters, create the first draft. In this version, write what you expect to find from your research.

Clearly separate your independent and dependent variables and the link between them. Don't fixate on syntax at this stage. The goal is to ensure your hypothesis addresses the issue.

5. Proof your hypothesis

After preparing the first draft of your hypothesis, you need to inspect it thoroughly. It should tick all the boxes, like being concise, straightforward, relevant, and accurate. Your final hypothesis has to be well-structured as well.

Research projects are an exciting and crucial part of being a scholar. And once you have your research question, you need a great hypothesis to begin conducting research. Thus, knowing how to write a hypothesis is very important.

Now that you have a firmer grasp on what a good hypothesis constitutes, the different kinds there are, and what process to follow, you will find it much easier to write your hypothesis, which ultimately helps your research.

Now it's easier than ever to streamline your research workflow with SciSpace Discover . Its integrated, comprehensive end-to-end platform for research allows scholars to easily discover, write and publish their research and fosters collaboration.

It includes everything you need, including a repository of over 270 million research papers across disciplines, SEO-optimized summaries and public profiles to show your expertise and experience.

If you found these tips on writing a research hypothesis useful, head over to our blog on Statistical Hypothesis Testing to learn about the top researchers, papers, and institutions in this domain.

Frequently Asked Questions (FAQs)

1. what is the definition of hypothesis.

According to the Oxford dictionary, a hypothesis is defined as “An idea or explanation of something that is based on a few known facts, but that has not yet been proved to be true or correct”.

2. What is an example of hypothesis?

The hypothesis is a statement that proposes a relationship between two or more variables. An example: "If we increase the number of new users who join our platform by 25%, then we will see an increase in revenue."

3. What is an example of null hypothesis?

A null hypothesis is a statement that there is no relationship between two variables. The null hypothesis is written as H0. The null hypothesis states that there is no effect. For example, if you're studying whether or not a particular type of exercise increases strength, your null hypothesis will be "there is no difference in strength between people who exercise and people who don't."

4. What are the types of research?

• Fundamental research

• Applied research

• Qualitative research

• Quantitative research

• Mixed research

• Exploratory research

• Longitudinal research

• Cross-sectional research

• Field research

• Laboratory research

• Fixed research

• Flexible research

• Action research

• Policy research

• Classification research

• Comparative research

• Causal research

• Inductive research

• Deductive research

5. How to write a hypothesis?

• Your hypothesis should be able to predict the relationship and outcome.

• Avoid wordiness by keeping it simple and brief.

• Your hypothesis should contain observable and testable outcomes.

• Your hypothesis should be relevant to the research question.

6. What are the 2 types of hypothesis?

• Null hypotheses are used to test the claim that "there is no difference between two groups of data".

• Alternative hypotheses test the claim that "there is a difference between two data groups".

7. Difference between research question and research hypothesis?

A research question is a broad, open-ended question you will try to answer through your research. A hypothesis is a statement based on prior research or theory that you expect to be true due to your study. Example - Research question: What are the factors that influence the adoption of the new technology? Research hypothesis: There is a positive relationship between age, education and income level with the adoption of the new technology.

8. What is plural for hypothesis?

The plural of hypothesis is hypotheses. Here's an example of how it would be used in a statement, "Numerous well-considered hypotheses are presented in this part, and they are supported by tables and figures that are well-illustrated."

9. What is the red queen hypothesis?

The red queen hypothesis in evolutionary biology states that species must constantly evolve to avoid extinction because if they don't, they will be outcompeted by other species that are evolving. Leigh Van Valen first proposed it in 1973; since then, it has been tested and substantiated many times.

10. Who is known as the father of null hypothesis?

The father of the null hypothesis is Sir Ronald Fisher. He published a paper in 1925 that introduced the concept of null hypothesis testing, and he was also the first to use the term itself.

11. When to reject null hypothesis?

You need to find a significant difference between your two populations to reject the null hypothesis. You can determine that by running statistical tests such as an independent sample t-test or a dependent sample t-test. You should reject the null hypothesis if the p-value is less than 0.05.

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Home » What is a Hypothesis – Types, Examples and Writing Guide

What is a Hypothesis – Types, Examples and Writing Guide

Table of Contents

Definition:

Hypothesis is an educated guess or proposed explanation for a phenomenon, based on some initial observations or data. It is a tentative statement that can be tested and potentially proven or disproven through further investigation and experimentation.

Hypothesis is often used in scientific research to guide the design of experiments and the collection and analysis of data. It is an essential element of the scientific method, as it allows researchers to make predictions about the outcome of their experiments and to test those predictions to determine their accuracy.

Types of Hypothesis

Types of Hypothesis are as follows:

Research Hypothesis

A research hypothesis is a statement that predicts a relationship between variables. It is usually formulated as a specific statement that can be tested through research, and it is often used in scientific research to guide the design of experiments.

Null Hypothesis

The null hypothesis is a statement that assumes there is no significant difference or relationship between variables. It is often used as a starting point for testing the research hypothesis, and if the results of the study reject the null hypothesis, it suggests that there is a significant difference or relationship between variables.

Alternative Hypothesis

An alternative hypothesis is a statement that assumes there is a significant difference or relationship between variables. It is often used as an alternative to the null hypothesis and is tested against the null hypothesis to determine which statement is more accurate.

Directional Hypothesis

A directional hypothesis is a statement that predicts the direction of the relationship between variables. For example, a researcher might predict that increasing the amount of exercise will result in a decrease in body weight.

Non-directional Hypothesis

A non-directional hypothesis is a statement that predicts the relationship between variables but does not specify the direction. For example, a researcher might predict that there is a relationship between the amount of exercise and body weight, but they do not specify whether increasing or decreasing exercise will affect body weight.

Statistical Hypothesis

A statistical hypothesis is a statement that assumes a particular statistical model or distribution for the data. It is often used in statistical analysis to test the significance of a particular result.

Composite Hypothesis

A composite hypothesis is a statement that assumes more than one condition or outcome. It can be divided into several sub-hypotheses, each of which represents a different possible outcome.

Empirical Hypothesis

An empirical hypothesis is a statement that is based on observed phenomena or data. It is often used in scientific research to develop theories or models that explain the observed phenomena.

Simple Hypothesis

A simple hypothesis is a statement that assumes only one outcome or condition. It is often used in scientific research to test a single variable or factor.

Complex Hypothesis

A complex hypothesis is a statement that assumes multiple outcomes or conditions. It is often used in scientific research to test the effects of multiple variables or factors on a particular outcome.

Applications of Hypothesis

Hypotheses are used in various fields to guide research and make predictions about the outcomes of experiments or observations. Here are some examples of how hypotheses are applied in different fields:

• Science : In scientific research, hypotheses are used to test the validity of theories and models that explain natural phenomena. For example, a hypothesis might be formulated to test the effects of a particular variable on a natural system, such as the effects of climate change on an ecosystem.
• Medicine : In medical research, hypotheses are used to test the effectiveness of treatments and therapies for specific conditions. For example, a hypothesis might be formulated to test the effects of a new drug on a particular disease.
• Psychology : In psychology, hypotheses are used to test theories and models of human behavior and cognition. For example, a hypothesis might be formulated to test the effects of a particular stimulus on the brain or behavior.
• Sociology : In sociology, hypotheses are used to test theories and models of social phenomena, such as the effects of social structures or institutions on human behavior. For example, a hypothesis might be formulated to test the effects of income inequality on crime rates.
• Business : In business research, hypotheses are used to test the validity of theories and models that explain business phenomena, such as consumer behavior or market trends. For example, a hypothesis might be formulated to test the effects of a new marketing campaign on consumer buying behavior.
• Engineering : In engineering, hypotheses are used to test the effectiveness of new technologies or designs. For example, a hypothesis might be formulated to test the efficiency of a new solar panel design.

How to write a Hypothesis

Here are the steps to follow when writing a hypothesis:

Identify the Research Question

The first step is to identify the research question that you want to answer through your study. This question should be clear, specific, and focused. It should be something that can be investigated empirically and that has some relevance or significance in the field.

Conduct a Literature Review

Before writing your hypothesis, it’s essential to conduct a thorough literature review to understand what is already known about the topic. This will help you to identify the research gap and formulate a hypothesis that builds on existing knowledge.

Determine the Variables

The next step is to identify the variables involved in the research question. A variable is any characteristic or factor that can vary or change. There are two types of variables: independent and dependent. The independent variable is the one that is manipulated or changed by the researcher, while the dependent variable is the one that is measured or observed as a result of the independent variable.

Formulate the Hypothesis

Based on the research question and the variables involved, you can now formulate your hypothesis. A hypothesis should be a clear and concise statement that predicts the relationship between the variables. It should be testable through empirical research and based on existing theory or evidence.

Write the Null Hypothesis

The null hypothesis is the opposite of the alternative hypothesis, which is the hypothesis that you are testing. The null hypothesis states that there is no significant difference or relationship between the variables. It is important to write the null hypothesis because it allows you to compare your results with what would be expected by chance.

Refine the Hypothesis

After formulating the hypothesis, it’s important to refine it and make it more precise. This may involve clarifying the variables, specifying the direction of the relationship, or making the hypothesis more testable.

Examples of Hypothesis

Here are a few examples of hypotheses in different fields:

• Psychology : “Increased exposure to violent video games leads to increased aggressive behavior in adolescents.”
• Biology : “Higher levels of carbon dioxide in the atmosphere will lead to increased plant growth.”
• Sociology : “Individuals who grow up in households with higher socioeconomic status will have higher levels of education and income as adults.”
• Education : “Implementing a new teaching method will result in higher student achievement scores.”
• Marketing : “Customers who receive a personalized email will be more likely to make a purchase than those who receive a generic email.”
• Physics : “An increase in temperature will cause an increase in the volume of a gas, assuming all other variables remain constant.”
• Medicine : “Consuming a diet high in saturated fats will increase the risk of developing heart disease.”

Purpose of Hypothesis

The purpose of a hypothesis is to provide a testable explanation for an observed phenomenon or a prediction of a future outcome based on existing knowledge or theories. A hypothesis is an essential part of the scientific method and helps to guide the research process by providing a clear focus for investigation. It enables scientists to design experiments or studies to gather evidence and data that can support or refute the proposed explanation or prediction.

The formulation of a hypothesis is based on existing knowledge, observations, and theories, and it should be specific, testable, and falsifiable. A specific hypothesis helps to define the research question, which is important in the research process as it guides the selection of an appropriate research design and methodology. Testability of the hypothesis means that it can be proven or disproven through empirical data collection and analysis. Falsifiability means that the hypothesis should be formulated in such a way that it can be proven wrong if it is incorrect.

In addition to guiding the research process, the testing of hypotheses can lead to new discoveries and advancements in scientific knowledge. When a hypothesis is supported by the data, it can be used to develop new theories or models to explain the observed phenomenon. When a hypothesis is not supported by the data, it can help to refine existing theories or prompt the development of new hypotheses to explain the phenomenon.

When to use Hypothesis

Here are some common situations in which hypotheses are used:

• In scientific research , hypotheses are used to guide the design of experiments and to help researchers make predictions about the outcomes of those experiments.
• In social science research , hypotheses are used to test theories about human behavior, social relationships, and other phenomena.
• I n business , hypotheses can be used to guide decisions about marketing, product development, and other areas. For example, a hypothesis might be that a new product will sell well in a particular market, and this hypothesis can be tested through market research.

Characteristics of Hypothesis

Here are some common characteristics of a hypothesis:

• Testable : A hypothesis must be able to be tested through observation or experimentation. This means that it must be possible to collect data that will either support or refute the hypothesis.
• Falsifiable : A hypothesis must be able to be proven false if it is not supported by the data. If a hypothesis cannot be falsified, then it is not a scientific hypothesis.
• Clear and concise : A hypothesis should be stated in a clear and concise manner so that it can be easily understood and tested.
• Based on existing knowledge : A hypothesis should be based on existing knowledge and research in the field. It should not be based on personal beliefs or opinions.
• Specific : A hypothesis should be specific in terms of the variables being tested and the predicted outcome. This will help to ensure that the research is focused and well-designed.
• Tentative: A hypothesis is a tentative statement or assumption that requires further testing and evidence to be confirmed or refuted. It is not a final conclusion or assertion.
• Relevant : A hypothesis should be relevant to the research question or problem being studied. It should address a gap in knowledge or provide a new perspective on the issue.

Advantages of Hypothesis

Hypotheses have several advantages in scientific research and experimentation:

• Guides research: A hypothesis provides a clear and specific direction for research. It helps to focus the research question, select appropriate methods and variables, and interpret the results.
• Predictive powe r: A hypothesis makes predictions about the outcome of research, which can be tested through experimentation. This allows researchers to evaluate the validity of the hypothesis and make new discoveries.
• Facilitates communication: A hypothesis provides a common language and framework for scientists to communicate with one another about their research. This helps to facilitate the exchange of ideas and promotes collaboration.
• Efficient use of resources: A hypothesis helps researchers to use their time, resources, and funding efficiently by directing them towards specific research questions and methods that are most likely to yield results.
• Provides a basis for further research: A hypothesis that is supported by data provides a basis for further research and exploration. It can lead to new hypotheses, theories, and discoveries.
• Increases objectivity: A hypothesis can help to increase objectivity in research by providing a clear and specific framework for testing and interpreting results. This can reduce bias and increase the reliability of research findings.

Limitations of Hypothesis

Some Limitations of the Hypothesis are as follows:

• Limited to observable phenomena: Hypotheses are limited to observable phenomena and cannot account for unobservable or intangible factors. This means that some research questions may not be amenable to hypothesis testing.
• May be inaccurate or incomplete: Hypotheses are based on existing knowledge and research, which may be incomplete or inaccurate. This can lead to flawed hypotheses and erroneous conclusions.
• May be biased: Hypotheses may be biased by the researcher’s own beliefs, values, or assumptions. This can lead to selective interpretation of data and a lack of objectivity in research.
• Cannot prove causation: A hypothesis can only show a correlation between variables, but it cannot prove causation. This requires further experimentation and analysis.
• Limited to specific contexts: Hypotheses are limited to specific contexts and may not be generalizable to other situations or populations. This means that results may not be applicable in other contexts or may require further testing.
• May be affected by chance : Hypotheses may be affected by chance or random variation, which can obscure or distort the true relationship between variables.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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A research hypothesis, in its plural form “hypotheses,” is a specific, testable prediction about the anticipated results of a study, established at its outset. It is a key component of the scientific method .

Hypotheses connect theory to data and guide the research process towards expanding scientific understanding

Some key points about hypotheses:

• A hypothesis expresses an expected pattern or relationship. It connects the variables under investigation.
• It is stated in clear, precise terms before any data collection or analysis occurs. This makes the hypothesis testable.
• A hypothesis must be falsifiable. It should be possible, even if unlikely in practice, to collect data that disconfirms rather than supports the hypothesis.
• Hypotheses guide research. Scientists design studies to explicitly evaluate hypotheses about how nature works.
• For a hypothesis to be valid, it must be testable against empirical evidence. The evidence can then confirm or disprove the testable predictions.
• Hypotheses are informed by background knowledge and observation, but go beyond what is already known to propose an explanation of how or why something occurs.

Predictions typically arise from a thorough knowledge of the research literature, curiosity about real-world problems or implications, and integrating this to advance theory. They build on existing literature while providing new insight.

Types of Research Hypotheses

Alternative hypothesis.

The research hypothesis is often called the alternative or experimental hypothesis in experimental research.

It typically suggests a potential relationship between two key variables: the independent variable, which the researcher manipulates, and the dependent variable, which is measured based on those changes.

The alternative hypothesis states a relationship exists between the two variables being studied (one variable affects the other).

A hypothesis is a testable statement or prediction about the relationship between two or more variables. It is a key component of the scientific method. Some key points about hypotheses:

• Important hypotheses lead to predictions that can be tested empirically. The evidence can then confirm or disprove the testable predictions.

In summary, a hypothesis is a precise, testable statement of what researchers expect to happen in a study and why. Hypotheses connect theory to data and guide the research process towards expanding scientific understanding.

An experimental hypothesis predicts what change(s) will occur in the dependent variable when the independent variable is manipulated.

It states that the results are not due to chance and are significant in supporting the theory being investigated.

The alternative hypothesis can be directional, indicating a specific direction of the effect, or non-directional, suggesting a difference without specifying its nature. It’s what researchers aim to support or demonstrate through their study.

Null Hypothesis

The null hypothesis states no relationship exists between the two variables being studied (one variable does not affect the other). There will be no changes in the dependent variable due to manipulating the independent variable.

It states results are due to chance and are not significant in supporting the idea being investigated.

The null hypothesis, positing no effect or relationship, is a foundational contrast to the research hypothesis in scientific inquiry. It establishes a baseline for statistical testing, promoting objectivity by initiating research from a neutral stance.

Many statistical methods are tailored to test the null hypothesis, determining the likelihood of observed results if no true effect exists.

This dual-hypothesis approach provides clarity, ensuring that research intentions are explicit, and fosters consistency across scientific studies, enhancing the standardization and interpretability of research outcomes.

Nondirectional Hypothesis

A non-directional hypothesis, also known as a two-tailed hypothesis, predicts that there is a difference or relationship between two variables but does not specify the direction of this relationship.

It merely indicates that a change or effect will occur without predicting which group will have higher or lower values.

For example, “There is a difference in performance between Group A and Group B” is a non-directional hypothesis.

Directional Hypothesis

A directional (one-tailed) hypothesis predicts the nature of the effect of the independent variable on the dependent variable. It predicts in which direction the change will take place. (i.e., greater, smaller, less, more)

It specifies whether one variable is greater, lesser, or different from another, rather than just indicating that there’s a difference without specifying its nature.

For example, “Exercise increases weight loss” is a directional hypothesis.

Falsifiability

The Falsification Principle, proposed by Karl Popper , is a way of demarcating science from non-science. It suggests that for a theory or hypothesis to be considered scientific, it must be testable and irrefutable.

Falsifiability emphasizes that scientific claims shouldn’t just be confirmable but should also have the potential to be proven wrong.

It means that there should exist some potential evidence or experiment that could prove the proposition false.

However many confirming instances exist for a theory, it only takes one counter observation to falsify it. For example, the hypothesis that “all swans are white,” can be falsified by observing a black swan.

For Popper, science should attempt to disprove a theory rather than attempt to continually provide evidence to support a research hypothesis.

Can a Hypothesis be Proven?

Hypotheses make probabilistic predictions. They state the expected outcome if a particular relationship exists. However, a study result supporting a hypothesis does not definitively prove it is true.

All studies have limitations. There may be unknown confounding factors or issues that limit the certainty of conclusions. Additional studies may yield different results.

In science, hypotheses can realistically only be supported with some degree of confidence, not proven. The process of science is to incrementally accumulate evidence for and against hypothesized relationships in an ongoing pursuit of better models and explanations that best fit the empirical data. But hypotheses remain open to revision and rejection if that is where the evidence leads.

• Disproving a hypothesis is definitive. Solid disconfirmatory evidence will falsify a hypothesis and require altering or discarding it based on the evidence.
• However, confirming evidence is always open to revision. Other explanations may account for the same results, and additional or contradictory evidence may emerge over time.

We can never 100% prove the alternative hypothesis. Instead, we see if we can disprove, or reject the null hypothesis.

If we reject the null hypothesis, this doesn’t mean that our alternative hypothesis is correct but does support the alternative/experimental hypothesis.

Upon analysis of the results, an alternative hypothesis can be rejected or supported, but it can never be proven to be correct. We must avoid any reference to results proving a theory as this implies 100% certainty, and there is always a chance that evidence may exist which could refute a theory.

How to Write a Hypothesis

• Identify variables . The researcher manipulates the independent variable and the dependent variable is the measured outcome.
• Operationalized the variables being investigated . Operationalization of a hypothesis refers to the process of making the variables physically measurable or testable, e.g. if you are about to study aggression, you might count the number of punches given by participants.
• Decide on a direction for your prediction . If there is evidence in the literature to support a specific effect of the independent variable on the dependent variable, write a directional (one-tailed) hypothesis. If there are limited or ambiguous findings in the literature regarding the effect of the independent variable on the dependent variable, write a non-directional (two-tailed) hypothesis.
• Make it Testable : Ensure your hypothesis can be tested through experimentation or observation. It should be possible to prove it false (principle of falsifiability).
• Clear & concise language . A strong hypothesis is concise (typically one to two sentences long), and formulated using clear and straightforward language, ensuring it’s easily understood and testable.

Consider a hypothesis many teachers might subscribe to: students work better on Monday morning than on Friday afternoon (IV=Day, DV= Standard of work).

Now, if we decide to study this by giving the same group of students a lesson on a Monday morning and a Friday afternoon and then measuring their immediate recall of the material covered in each session, we would end up with the following:

• The alternative hypothesis states that students will recall significantly more information on a Monday morning than on a Friday afternoon.
• The null hypothesis states that there will be no significant difference in the amount recalled on a Monday morning compared to a Friday afternoon. Any difference will be due to chance or confounding factors.

More Examples

• Memory : Participants exposed to classical music during study sessions will recall more items from a list than those who studied in silence.
• Social Psychology : Individuals who frequently engage in social media use will report higher levels of perceived social isolation compared to those who use it infrequently.
• Developmental Psychology : Children who engage in regular imaginative play have better problem-solving skills than those who don’t.
• Clinical Psychology : Cognitive-behavioral therapy will be more effective in reducing symptoms of anxiety over a 6-month period compared to traditional talk therapy.
• Cognitive Psychology : Individuals who multitask between various electronic devices will have shorter attention spans on focused tasks than those who single-task.
• Health Psychology : Patients who practice mindfulness meditation will experience lower levels of chronic pain compared to those who don’t meditate.
• Organizational Psychology : Employees in open-plan offices will report higher levels of stress than those in private offices.
• Behavioral Psychology : Rats rewarded with food after pressing a lever will press it more frequently than rats who receive no reward.

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How to Write a Great Hypothesis

Hypothesis Definition, Format, Examples, and Tips

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Amy Morin, LCSW, is a psychotherapist and international bestselling author. Her books, including "13 Things Mentally Strong People Don't Do," have been translated into more than 40 languages. Her TEDx talk,  "The Secret of Becoming Mentally Strong," is one of the most viewed talks of all time.

Verywell / Alex Dos Diaz

• The Scientific Method

Hypothesis Format

Falsifiability of a hypothesis.

• Operationalization

Hypothesis Types

Hypotheses examples.

• Collecting Data

A hypothesis is a tentative statement about the relationship between two or more variables. It is a specific, testable prediction about what you expect to happen in a study. It is a preliminary answer to your question that helps guide the research process.

Consider a study designed to examine the relationship between sleep deprivation and test performance. The hypothesis might be: "This study is designed to assess the hypothesis that sleep-deprived people will perform worse on a test than individuals who are not sleep-deprived."

At a Glance

A hypothesis is crucial to scientific research because it offers a clear direction for what the researchers are looking to find. This allows them to design experiments to test their predictions and add to our scientific knowledge about the world. This article explores how a hypothesis is used in psychology research, how to write a good hypothesis, and the different types of hypotheses you might use.

The Hypothesis in the Scientific Method

In the scientific method , whether it involves research in psychology, biology, or some other area, a hypothesis represents what the researchers think will happen in an experiment. The scientific method involves the following steps:

• Forming a question
• Performing background research
• Creating a hypothesis
• Designing an experiment
• Collecting data
• Analyzing the results
• Drawing conclusions
• Communicating the results

The hypothesis is a prediction, but it involves more than a guess. Most of the time, the hypothesis begins with a question which is then explored through background research. At this point, researchers then begin to develop a testable hypothesis.

Unless you are creating an exploratory study, your hypothesis should always explain what you  expect  to happen.

In a study exploring the effects of a particular drug, the hypothesis might be that researchers expect the drug to have some type of effect on the symptoms of a specific illness. In psychology, the hypothesis might focus on how a certain aspect of the environment might influence a particular behavior.

Remember, a hypothesis does not have to be correct. While the hypothesis predicts what the researchers expect to see, the goal of the research is to determine whether this guess is right or wrong. When conducting an experiment, researchers might explore numerous factors to determine which ones might contribute to the ultimate outcome.

In many cases, researchers may find that the results of an experiment  do not  support the original hypothesis. When writing up these results, the researchers might suggest other options that should be explored in future studies.

In many cases, researchers might draw a hypothesis from a specific theory or build on previous research. For example, prior research has shown that stress can impact the immune system. So a researcher might hypothesize: "People with high-stress levels will be more likely to contract a common cold after being exposed to the virus than people who have low-stress levels."

In other instances, researchers might look at commonly held beliefs or folk wisdom. "Birds of a feather flock together" is one example of folk adage that a psychologist might try to investigate. The researcher might pose a specific hypothesis that "People tend to select romantic partners who are similar to them in interests and educational level."

Elements of a Good Hypothesis

So how do you write a good hypothesis? When trying to come up with a hypothesis for your research or experiments, ask yourself the following questions:

• Is your hypothesis based on your research on a topic?
• Can your hypothesis be tested?
• Does your hypothesis include independent and dependent variables?

Before you come up with a specific hypothesis, spend some time doing background research. Once you have completed a literature review, start thinking about potential questions you still have. Pay attention to the discussion section in the  journal articles you read . Many authors will suggest questions that still need to be explored.

How to Formulate a Good Hypothesis

To form a hypothesis, you should take these steps:

• Collect as many observations about a topic or problem as you can.
• Evaluate these observations and look for possible causes of the problem.
• Create a list of possible explanations that you might want to explore.
• After you have developed some possible hypotheses, think of ways that you could confirm or disprove each hypothesis through experimentation. This is known as falsifiability.

In the scientific method ,  falsifiability is an important part of any valid hypothesis. In order to test a claim scientifically, it must be possible that the claim could be proven false.

Students sometimes confuse the idea of falsifiability with the idea that it means that something is false, which is not the case. What falsifiability means is that  if  something was false, then it is possible to demonstrate that it is false.

One of the hallmarks of pseudoscience is that it makes claims that cannot be refuted or proven false.

The Importance of Operational Definitions

A variable is a factor or element that can be changed and manipulated in ways that are observable and measurable. However, the researcher must also define how the variable will be manipulated and measured in the study.

Operational definitions are specific definitions for all relevant factors in a study. This process helps make vague or ambiguous concepts detailed and measurable.

For example, a researcher might operationally define the variable " test anxiety " as the results of a self-report measure of anxiety experienced during an exam. A "study habits" variable might be defined by the amount of studying that actually occurs as measured by time.

These precise descriptions are important because many things can be measured in various ways. Clearly defining these variables and how they are measured helps ensure that other researchers can replicate your results.

Replicability

One of the basic principles of any type of scientific research is that the results must be replicable.

Replication means repeating an experiment in the same way to produce the same results. By clearly detailing the specifics of how the variables were measured and manipulated, other researchers can better understand the results and repeat the study if needed.

Some variables are more difficult than others to define. For example, how would you operationally define a variable such as aggression ? For obvious ethical reasons, researchers cannot create a situation in which a person behaves aggressively toward others.

To measure this variable, the researcher must devise a measurement that assesses aggressive behavior without harming others. The researcher might utilize a simulated task to measure aggressiveness in this situation.

Hypothesis Checklist

• Does your hypothesis focus on something that you can actually test?
• Does your hypothesis include both an independent and dependent variable?
• Can you manipulate the variables?
• Can your hypothesis be tested without violating ethical standards?

The hypothesis you use will depend on what you are investigating and hoping to find. Some of the main types of hypotheses that you might use include:

• Simple hypothesis : This type of hypothesis suggests there is a relationship between one independent variable and one dependent variable.
• Complex hypothesis : This type suggests a relationship between three or more variables, such as two independent and dependent variables.
• Null hypothesis : This hypothesis suggests no relationship exists between two or more variables.
• Alternative hypothesis : This hypothesis states the opposite of the null hypothesis.
• Statistical hypothesis : This hypothesis uses statistical analysis to evaluate a representative population sample and then generalizes the findings to the larger group.
• Logical hypothesis : This hypothesis assumes a relationship between variables without collecting data or evidence.

A hypothesis often follows a basic format of "If {this happens} then {this will happen}." One way to structure your hypothesis is to describe what will happen to the  dependent variable  if you change the  independent variable .

The basic format might be: "If {these changes are made to a certain independent variable}, then we will observe {a change in a specific dependent variable}."

A few examples of simple hypotheses:

• "Students who eat breakfast will perform better on a math exam than students who do not eat breakfast."
• "Students who experience test anxiety before an English exam will get lower scores than students who do not experience test anxiety."​
• "Motorists who talk on the phone while driving will be more likely to make errors on a driving course than those who do not talk on the phone."
• "Children who receive a new reading intervention will have higher reading scores than students who do not receive the intervention."

Examples of a complex hypothesis include:

• "People with high-sugar diets and sedentary activity levels are more likely to develop depression."
• "Younger people who are regularly exposed to green, outdoor areas have better subjective well-being than older adults who have limited exposure to green spaces."

Examples of a null hypothesis include:

• "There is no difference in anxiety levels between people who take St. John's wort supplements and those who do not."
• "There is no difference in scores on a memory recall task between children and adults."
• "There is no difference in aggression levels between children who play first-person shooter games and those who do not."

Examples of an alternative hypothesis:

• "People who take St. John's wort supplements will have less anxiety than those who do not."
• "Adults will perform better on a memory task than children."
• "Children who play first-person shooter games will show higher levels of aggression than children who do not." 

Collecting Data on Your Hypothesis

Once a researcher has formed a testable hypothesis, the next step is to select a research design and start collecting data. The research method depends largely on exactly what they are studying. There are two basic types of research methods: descriptive research and experimental research.

Descriptive Research Methods

Descriptive research such as  case studies ,  naturalistic observations , and surveys are often used when  conducting an experiment is difficult or impossible. These methods are best used to describe different aspects of a behavior or psychological phenomenon.

Once a researcher has collected data using descriptive methods, a  correlational study  can examine how the variables are related. This research method might be used to investigate a hypothesis that is difficult to test experimentally.

Experimental Research Methods

Experimental methods  are used to demonstrate causal relationships between variables. In an experiment, the researcher systematically manipulates a variable of interest (known as the independent variable) and measures the effect on another variable (known as the dependent variable).

Unlike correlational studies, which can only be used to determine if there is a relationship between two variables, experimental methods can be used to determine the actual nature of the relationship—whether changes in one variable actually  cause  another to change.

The hypothesis is a critical part of any scientific exploration. It represents what researchers expect to find in a study or experiment. In situations where the hypothesis is unsupported by the research, the research still has value. Such research helps us better understand how different aspects of the natural world relate to one another. It also helps us develop new hypotheses that can then be tested in the future.

Thompson WH, Skau S. On the scope of scientific hypotheses .  R Soc Open Sci . 2023;10(8):230607. doi:10.1098/rsos.230607

Taran S, Adhikari NKJ, Fan E. Falsifiability in medicine: what clinicians can learn from Karl Popper [published correction appears in Intensive Care Med. 2021 Jun 17;:].  Intensive Care Med . 2021;47(9):1054-1056. doi:10.1007/s00134-021-06432-z

Eyler AA. Research Methods for Public Health . 1st ed. Springer Publishing Company; 2020. doi:10.1891/9780826182067.0004

Nosek BA, Errington TM. What is replication ?  PLoS Biol . 2020;18(3):e3000691. doi:10.1371/journal.pbio.3000691

Aggarwal R, Ranganathan P. Study designs: Part 2 - Descriptive studies .  Perspect Clin Res . 2019;10(1):34-36. doi:10.4103/picr.PICR_154_18

Nevid J. Psychology: Concepts and Applications. Wadworth, 2013.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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Research Hypothesis: What It Is, Types + How to Develop?

A research study starts with a question. Researchers worldwide ask questions and create research hypotheses. The effectiveness of research relies on developing a good research hypothesis. Examples of research hypotheses can guide researchers in writing effective ones.

In this blog, we’ll learn what a research hypothesis is, why it’s important in research, and the different types used in science. We’ll also guide you through creating your research hypothesis and discussing ways to test and evaluate it.

What is a Research Hypothesis?

A hypothesis is like a guess or idea that you suggest to check if it’s true. A research hypothesis is a statement that brings up a question and predicts what might happen.

It’s really important in the scientific method and is used in experiments to figure things out. Essentially, it’s an educated guess about how things are connected in the research.

A research hypothesis usually includes pointing out the independent variable (the thing they’re changing or studying) and the dependent variable (the result they’re measuring or watching). It helps plan how to gather and analyze data to see if there’s evidence to support or deny the expected connection between these variables.

Importance of Hypothesis in Research

Hypotheses are really important in research. They help design studies, allow for practical testing, and add to our scientific knowledge. Their main role is to organize research projects, making them purposeful, focused, and valuable to the scientific community. Let’s look at some key reasons why they matter:

• A research hypothesis helps test theories.

A hypothesis plays a pivotal role in the scientific method by providing a basis for testing existing theories. For example, a hypothesis might test the predictive power of a psychological theory on human behavior.

• It serves as a great platform for investigation activities.

It serves as a launching pad for investigation activities, which offers researchers a clear starting point. A research hypothesis can explore the relationship between exercise and stress reduction.

• Hypothesis guides the research work or study.

A well-formulated hypothesis guides the entire research process. It ensures that the study remains focused and purposeful. For instance, a hypothesis about the impact of social media on interpersonal relationships provides clear guidance for a study.

• Hypothesis sometimes suggests theories.

In some cases, a hypothesis can suggest new theories or modifications to existing ones. For example, a hypothesis testing the effectiveness of a new drug might prompt a reconsideration of current medical theories.

• It helps in knowing the data needs.

A hypothesis clarifies the data requirements for a study, ensuring that researchers collect the necessary information—a hypothesis guiding the collection of demographic data to analyze the influence of age on a particular phenomenon.

• The hypothesis explains social phenomena.

Hypotheses are instrumental in explaining complex social phenomena. For instance, a hypothesis might explore the relationship between economic factors and crime rates in a given community.

• Hypothesis provides a relationship between phenomena for empirical Testing.

Hypotheses establish clear relationships between phenomena, paving the way for empirical testing. An example could be a hypothesis exploring the correlation between sleep patterns and academic performance.

• It helps in knowing the most suitable analysis technique.

A hypothesis guides researchers in selecting the most appropriate analysis techniques for their data. For example, a hypothesis focusing on the effectiveness of a teaching method may lead to the choice of statistical analyses best suited for educational research.

Characteristics of a Good Research Hypothesis

A hypothesis is a specific idea that you can test in a study. It often comes from looking at past research and theories. A good hypothesis usually starts with a research question that you can explore through background research. For it to be effective, consider these key characteristics:

• Clear and Focused Language: A good hypothesis uses clear and focused language to avoid confusion and ensure everyone understands it.
• Related to the Research Topic: The hypothesis should directly relate to the research topic, acting as a bridge between the specific question and the broader study.
• Testable: An effective hypothesis can be tested, meaning its prediction can be checked with real data to support or challenge the proposed relationship.
• Potential for Exploration: A good hypothesis often comes from a research question that invites further exploration. Doing background research helps find gaps and potential areas to investigate.
• Includes Variables: The hypothesis should clearly state both the independent and dependent variables, specifying the factors being studied and the expected outcomes.
• Ethical Considerations: Check if variables can be manipulated without breaking ethical standards. It’s crucial to maintain ethical research practices.
• Predicts Outcomes: The hypothesis should predict the expected relationship and outcome, acting as a roadmap for the study and guiding data collection and analysis.
• Simple and Concise: A good hypothesis avoids unnecessary complexity and is simple and concise, expressing the essence of the proposed relationship clearly.
• Clear and Assumption-Free: The hypothesis should be clear and free from assumptions about the reader’s prior knowledge, ensuring universal understanding.
• Observable and Testable Results: A strong hypothesis implies research that produces observable and testable results, making sure the study’s outcomes can be effectively measured and analyzed.

When you use these characteristics as a checklist, it can help you create a good research hypothesis. It’ll guide improving and strengthening the hypothesis, identifying any weaknesses, and making necessary changes. Crafting a hypothesis with these features helps you conduct a thorough and insightful research study.

Types of Research Hypotheses

The research hypothesis comes in various types, each serving a specific purpose in guiding the scientific investigation. Knowing the differences will make it easier for you to create your own hypothesis. Here’s an overview of the common types:

01. Null Hypothesis

The null hypothesis states that there is no connection between two considered variables or that two groups are unrelated. As discussed earlier, a hypothesis is an unproven assumption lacking sufficient supporting data. It serves as the statement researchers aim to disprove. It is testable, verifiable, and can be rejected.

For example, if you’re studying the relationship between Project A and Project B, assuming both projects are of equal standard is your null hypothesis. It needs to be specific for your study.

02. Alternative Hypothesis

The alternative hypothesis is basically another option to the null hypothesis. It involves looking for a significant change or alternative that could lead you to reject the null hypothesis. It’s a different idea compared to the null hypothesis.

When you create a null hypothesis, you’re making an educated guess about whether something is true or if there’s a connection between that thing and another variable. If the null view suggests something is correct, the alternative hypothesis says it’s incorrect. 

For instance, if your null hypothesis is “I’m going to be $1000 richer,” the alternative hypothesis would be “I’m not going to get $1000 or be richer.”

03. Directional Hypothesis

The directional hypothesis predicts the direction of the relationship between independent and dependent variables. They specify whether the effect will be positive or negative.

If you increase your study hours, you will experience a positive association with your exam scores. This hypothesis suggests that as you increase the independent variable (study hours), there will also be an increase in the dependent variable (exam scores).

04. Non-directional Hypothesis

The non-directional hypothesis predicts the existence of a relationship between variables but does not specify the direction of the effect. It suggests that there will be a significant difference or relationship, but it does not predict the nature of that difference.

For example, you will find no notable difference in test scores between students who receive the educational intervention and those who do not. However, once you compare the test scores of the two groups, you will notice an important difference.

05. Simple Hypothesis

A simple hypothesis predicts a relationship between one dependent variable and one independent variable without specifying the nature of that relationship. It’s simple and usually used when we don’t know much about how the two things are connected.

For example, if you adopt effective study habits, you will achieve higher exam scores than those with poor study habits.

06. Complex Hypothesis

A complex hypothesis is an idea that specifies a relationship between multiple independent and dependent variables. It is a more detailed idea than a simple hypothesis.

While a simple view suggests a straightforward cause-and-effect relationship between two things, a complex hypothesis involves many factors and how they’re connected to each other.

For example, when you increase your study time, you tend to achieve higher exam scores. The connection between your study time and exam performance is affected by various factors, including the quality of your sleep, your motivation levels, and the effectiveness of your study techniques.

If you sleep well, stay highly motivated, and use effective study strategies, you may observe a more robust positive correlation between the time you spend studying and your exam scores, unlike those who may lack these factors.

07. Associative Hypothesis

An associative hypothesis proposes a connection between two things without saying that one causes the other. Basically, it suggests that when one thing changes, the other changes too, but it doesn’t claim that one thing is causing the change in the other.

For example, you will likely notice higher exam scores when you increase your study time. You can recognize an association between your study time and exam scores in this scenario.

Your hypothesis acknowledges a relationship between the two variables—your study time and exam scores—without asserting that increased study time directly causes higher exam scores. You need to consider that other factors, like motivation or learning style, could affect the observed association.

08. Causal Hypothesis

A causal hypothesis proposes a cause-and-effect relationship between two variables. It suggests that changes in one variable directly cause changes in another variable.

For example, when you increase your study time, you experience higher exam scores. This hypothesis suggests a direct cause-and-effect relationship, indicating that the more time you spend studying, the higher your exam scores. It assumes that changes in your study time directly influence changes in your exam performance.

09. Empirical Hypothesis

An empirical hypothesis is a statement based on things we can see and measure. It comes from direct observation or experiments and can be tested with real-world evidence. If an experiment proves a theory, it supports the idea and shows it’s not just a guess. This makes the statement more reliable than a wild guess.

For example, if you increase the dosage of a certain medication, you might observe a quicker recovery time for patients. Imagine you’re in charge of a clinical trial. In this trial, patients are given varying dosages of the medication, and you measure and compare their recovery times. This allows you to directly see the effects of different dosages on how fast patients recover.

This way, you can create a research hypothesis: “Increasing the dosage of a certain medication will lead to a faster recovery time for patients.”

10. Statistical Hypothesis

A statistical hypothesis is a statement or assumption about a population parameter that is the subject of an investigation. It serves as the basis for statistical analysis and testing. It is often tested using statistical methods to draw inferences about the larger population.

In a hypothesis test, statistical evidence is collected to either reject the null hypothesis in favor of the alternative hypothesis or fail to reject the null hypothesis due to insufficient evidence.

For example, let’s say you’re testing a new medicine. Your hypothesis could be that the medicine doesn’t really help patients get better. So, you collect data and use statistics to see if your guess is right or if the medicine actually makes a difference.

If the data strongly shows that the medicine does help, you say your guess was wrong, and the medicine does make a difference. But if the proof isn’t strong enough, you can stick with your original guess because you didn’t get enough evidence to change your mind.

How to Develop a Research Hypotheses?

Step 1: identify your research problem or topic..

Define the area of interest or the problem you want to investigate. Make sure it’s clear and well-defined.

Start by asking a question about your chosen topic. Consider the limitations of your research and create a straightforward problem related to your topic. Once you’ve done that, you can develop and test a hypothesis with evidence.

Step 2: Conduct a literature review

Review existing literature related to your research problem. This will help you understand the current state of knowledge in the field, identify gaps, and build a foundation for your hypothesis. Consider the following questions:

• What existing research has been conducted on your chosen topic?
• Are there any gaps or unanswered questions in the current literature?
• How will the existing literature contribute to the foundation of your research?

Step 3: Formulate your research question

Based on your literature review, create a specific and concise research question that addresses your identified problem. Your research question should be clear, focused, and relevant to your field of study.

Step 4: Identify variables

Determine the key variables involved in your research question. Variables are the factors or phenomena that you will study and manipulate to test your hypothesis.

• Independent Variable: The variable you manipulate or control.
• Dependent Variable: The variable you measure to observe the effect of the independent variable.

Step 5: State the Null hypothesis

The null hypothesis is a statement that there is no significant difference or effect. It serves as a baseline for comparison with the alternative hypothesis.

Step 6: Select appropriate methods for testing the hypothesis

Choose research methods that align with your study objectives, such as experiments, surveys, or observational studies. The selected methods enable you to test your research hypothesis effectively.

Creating a research hypothesis usually takes more than one try. Expect to make changes as you collect data. It’s normal to test and say no to a few hypotheses before you find the right answer to your research question.

Testing and Evaluating Hypotheses

Testing hypotheses is a really important part of research. It’s like the practical side of things. Here, real-world evidence will help you determine how different things are connected. Let’s explore the main steps in hypothesis testing:

• State your research hypothesis.

Before testing, clearly articulate your research hypothesis. This involves framing both a null hypothesis, suggesting no significant effect or relationship, and an alternative hypothesis, proposing the expected outcome.

• Collect data strategically.

Plan how you will gather information in a way that fits your study. Make sure your data collection method matches the things you’re studying.

Whether through surveys, observations, or experiments, this step demands precision and adherence to the established methodology. The quality of data collected directly influences the credibility of study outcomes.

• Perform an appropriate statistical test.

Choose a statistical test that aligns with the nature of your data and the hypotheses being tested. Whether it’s a t-test, chi-square test, ANOVA, or regression analysis, selecting the right statistical tool is paramount for accurate and reliable results.

• Decide if your idea was right or wrong.

Following the statistical analysis, evaluate the results in the context of your null hypothesis. You need to decide if you should reject your null hypothesis or not.

• Share what you found.

When discussing what you found in your research, be clear and organized. Say whether your idea was supported or not, and talk about what your results mean. Also, mention any limits to your study and suggest ideas for future research.

The Role of QuestionPro to Develop a Good Research Hypothesis

QuestionPro is a survey and research platform that provides tools for creating, distributing, and analyzing surveys. It plays a crucial role in the research process, especially when you’re in the initial stages of hypothesis development. Here’s how QuestionPro can help you to develop a good research hypothesis:

• Survey design and data collection: You can use the platform to create targeted questions that help you gather relevant data.
• Exploratory research: Through surveys and feedback mechanisms on QuestionPro, you can conduct exploratory research to understand the landscape of a particular subject.
• Literature review and background research: QuestionPro surveys can collect sample population opinions, experiences, and preferences. This data and a thorough literature evaluation can help you generate a well-grounded hypothesis by improving your research knowledge.
• Identifying variables: Using targeted survey questions, you can identify relevant variables related to their research topic.
• Testing assumptions: You can use surveys to informally test certain assumptions or hypotheses before formalizing a research hypothesis.
• Data analysis tools: QuestionPro provides tools for analyzing survey data. You can use these tools to identify the collected data’s patterns, correlations, or trends.
• Refining your hypotheses: As you collect data through QuestionPro, you can adjust your hypotheses based on the real-world responses you receive.

A research hypothesis is like a guide for researchers in science. It’s a well-thought-out idea that has been thoroughly tested. This idea is crucial as researchers can explore different fields, such as medicine, social sciences, and natural sciences. The research hypothesis links theories to real-world evidence and gives researchers a clear path to explore and make discoveries.

QuestionPro Research Suite is a helpful tool for researchers. It makes creating surveys, collecting data, and analyzing information easily. It supports all kinds of research, from exploring new ideas to forming hypotheses. With a focus on using data, it helps researchers do their best work.

Are you interested in learning more about QuestionPro Research Suite? Take advantage of QuestionPro’s free trial to get an initial look at its capabilities and realize the full potential of your research efforts.

LEARN MORE         FREE TRIAL

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Principles of Research Methodology pp 31–53 Cite as

The Research Hypothesis: Role and Construction

• Phyllis G. Supino EdD 3  
• First Online: 01 January 2012

5973 Accesses

A hypothesis is a logical construct, interposed between a problem and its solution, which represents a proposed answer to a research question. It gives direction to the investigator’s thinking about the problem and, therefore, facilitates a solution. There are three primary modes of inference by which hypotheses are developed: deduction (reasoning from a general propositions to specific instances), induction (reasoning from specific instances to a general proposition), and abduction (formulation/acceptance on probation of a hypothesis to explain a surprising observation).

A research hypothesis should reflect an inference about variables; be stated as a grammatically complete, declarative sentence; be expressed simply and unambiguously; provide an adequate answer to the research problem; and be testable. Hypotheses can be classified as conceptual versus operational, single versus bi- or multivariable, causal or not causal, mechanistic versus nonmechanistic, and null or alternative. Hypotheses most commonly entail statements about “variables” which, in turn, can be classified according to their level of measurement (scaling characteristics) or according to their role in the hypothesis (independent, dependent, moderator, control, or intervening).

A hypothesis is rendered operational when its broadly (conceptually) stated variables are replaced by operational definitions of those variables. Hypotheses stated in this manner are called operational hypotheses, specific hypotheses, or predictions and facilitate testing.

Wrong hypotheses, rightly worked from, have produced more results than unguided observation

—Augustus De Morgan, 1872[ 1 ]—

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Once a problem has been defined, the investigator can formulate a hypothesis (or set of hypotheses, if there are multiple subproblems) about the outcome of the study designed to resolve the problem. A hypothesis (from the Greek, foundation ) is a logical construct, interposed between a problem and its solution, which represents a proposed answer to a research question. It gives direction to the investigator’s thinking about the problem and, therefore, facilitates a solution. Unlike facts and assumptions (presumed true and, therefore, not tested in the study) or theory (a relatively well-supported unifying system explicating a broad spectrum of observations and inferences, including previously tested hypotheses), the research hypothesis is a reasoned but tentative proposition typically expressing a relation between variables. For it to be useful and, more importantly, assessable, it must generate predictions that can be tested by subsequent acquisition, analysis, and interpretation of data (i.e., through formal observation or experimentation). When the results of the study are as ­predicted, the hypothesis is ­supported. As noted below, such support does not necessarily indicate verification of the hypothesis. Consistent replication of predictions in subsequent studies may be needed if the hypothesis is to be accepted as a theory or a component of a theory. If results are not as predicted, the hypothesis is rejected (or, at minimum, revised or removed from active consideration until future developments in science and/or technology provide new tools for retesting). As Leedy has stated, a “hypothesis is to a researcher what a point of triangulation is to a surveyor: it provides a position from which he may orient his exploration into the unknown and a checkpoint against which to test his findings” [ 2 ]. The paramount role of the hypothesis for guiding biomedical investigations was first highlighted by the eminent physiologist Claude Bernard (1813–1878) [ 3 ]. In the current era, hypotheses are considered fundamental to rigorous research, and biomedical studies without hypotheses have been largely abandoned in favor of those designed to generate or test them [ 4 ].

Hypotheses Versus Assumptions

It is important to recognize the difference between a hypothesis and an assumption. These terms share the same etymological root and are often confused. An assumption is accepted as fact in designing or justifying a study (though it is likely to have been the subject of previous research). Thus, the investigator does not set out to test it. Examples of assumptions include:

Radionuclide cineangiography measures ventricular performance.

Chest x-rays measure the extent of lung infiltrates.

The SF-36 measures general health-related quality of life.

Medical education improves knowledge of clinical medicine.

An apple a day keeps the doctor away (the most famous [albeit untested] assumption of them all).

In contrast, the hypothesis is an expectation that an investigator will attempt to confirm through observation or experiment. Examples in clinical medicine include:

Among patients with chronic nonischemic mitral regurgitation (insufficiency), survival will be better among those whose valves have been repaired or replaced than among those who have been maintained on medical therapy.

Among patients hospitalized with community-acquired pneumonia, posthospital course will be better among those with a low-risk profile than among those with a high-risk profile before hospitalization.

Life expectancy will be greater among individuals consuming low-calorie diets than among those consuming high-calorie diets.

Health-related quality of life is better among those whose mitral valves have been repaired than among those whose mitral valves have been replaced.

Hypothesis Generation: Modes of Inference

There is a paucity of empirical data regarding the way (or ways) in which hypotheses are formulated by scientists and even less information about whether these methods vary across disciplines. Nonetheless, philosophers and research methodologists have suggested three fundamentally different modes of inference: deduction, induction, and abduction [ 5 ]. These differ ­primarily according to (1) whether the origin of the hypothesis is a body of knowledge or ­theory (the “rationalist” perspective), an empirical event (the “inductivist” perspective), or some combination of the two (the “abductivist” perspective); (2) the logical structure of the argument; and (3) the probability of a correct conclusion.

Hypothesis by Deduction

Deduction (from the Latin de [“out of”] and dūcerė [“to draw or lead”]) is one of the oldest forms of logical argument. It was introduced by the ancient Greeks who believed that acquisition of scientific knowledge (insight into the principles and character of “natural substances” and their causes) could be achieved largely by the same logical processes used to prove the validity of mathematical propositions [ 6 ]. Today, deduction remains the predominant mode of formal inference in research in mathematics and in the “fundamental” sciences, but it also plays an important role in the empirical sciences. A deductively derived hypothesis arises directly from logical analysis of a theoretical framework, previously developed to provide an explanation of events or phenomena. It is considered to be nonampliative because, while it helps to provide proof of principle, it adds nothing new beyond the theory. The validity of a theory can never be directly examined. Therefore, scientists wishing to evaluate it, or to test its utility within a given (perhaps new) context, will formulate a conjecture (hypothesis) that can be subjected to empirical appraisal. In forming a hypothesis by deduction, the investigator typically moves from a general proposition to a more specific case that is thought to be subsumed by the generalization (i.e., from theory to a “conceptual” hypothesis or from a “conceptual” hypothesis to a precise prediction based on the hypothesis). Deductive arguments can be conditional or syllogistic (e.g., categorical [ all , some , or none ], disjunctive [ or ], or linear [ including a quantitative or qualitative comparison ]) and contain at least two premises (statements of ­“evidence”) and a conclusion. A well-known categorical syllogism and example are given below:

All As are B (e.g., All men are mortal)

C is an A (e.g., Socrates is a man)

∴ C is a B (e.g., Socrates is mortal)

If the premises of a deductive argument are true and the reasoning used to reach the conclusion is valid (i.e., the form of the argument is correct), it will necessarily follow that the conclusion is sound (i.e., the premises, if true, guarantee the conclusion). If the form of the deductive argument is invalid (i.e., the premises are such that they do not lead to the conclusion: e.g., Socrates is mortal, all cats are mortal, ∴ Socrates is a cat) and/or the premises are untrue (e.g., all mortals are men [or cats]), the conclusion will be unsound. It should be noted that deductive reasoning is the only form of logical argument to which the term “validity” is appropriate.

The theory from which the hypothesis is derived can be specific to the discipline or it can be “borrowed” from another discipline. Polit and Beck [ 7 ] provide two examples of deductively formulated hypotheses, germane to nursing, derived from general reinforcement theory which posits that behaviors that are rewarded tend to be learned or repeated:

Nursing home residents who are praised (reinforced) by nursing personnel for self-feeding require less assistance in feeding than those who are not praised.

Pediatric patients who are given a reward (e.g., a balloon or permission to watch television when they cooperate during nursing procedures) tend to be more cooperative during those procedures than unrewarded peers.

Deduction also is used to translate broad hypotheses such as these to more specific operational hypotheses (i.e., working hypotheses or predictions) that can be directly tested by observation or experiment. When empirical support is obtained for a hypothesis, this, in turn, strengthens the theory or body of knowledge from which the hypothesis was deduced.

Hypothesis by Induction

Not all hypotheses are derived from theory. Frequently, in the empirical sciences, patterns, trends, and associations are observed serendipitously in clinical settings or in preclinical laboratories or, purposively, through exploratory data analysis or other hypothesis-generating research. Sometimes, they may result from specific findings gleaned from the research literature. These observations may be generalized to produce inductively derived hypotheses that may serve as the basis for predicting future events, phenomena, or patterns. Induction (from the Latin in [meaning “into”] and dūcerė [“to draw or to lead”]) is defined by Jenicek and Hitchcock as “any method of logical analysis that proceeds from the particular to the general” [ 8 ] and represents the logical opposite of deduction which, as noted above, typically proceeds from the general to the specific. Induction can be used not only to formulate hypotheses but to confirm or refute them, which may be its most appropriate use, as noted below (see Abduction). Inductive reasoning, which is based heavily on the senses rather than on intellectual reflection, was popularized by the English philosopher and scientist, Sir Francis Bacon (1561–1626) [ 9 ], who proposed it as the logic of scientific discovery, a position that, subsequently, has been vigorously disputed by the Austrian logician, Sir Karl Popper (1902–1994) [ 10 ] and other philosophers of science. There are various forms of inductive inference. One of the most common is enumerative induction (or inductive generalization). Jenicek and Hitchcock [ 8 ] describe it as a mode by which “one concludes that all cases of a specified kind have a specified property on the basis of observation that all examined cases of that kind have the property” [ 8 ]. It is called “enumerative” because it itemizes cases in which some pattern is found and, solely for this reason (i.e., without the benefit of a theoretical framework), forecasts its recurrence. Other forms of induction include argument from analogy (forming inferences based on a shared property or properties of individual cases) or prediction (drawing conclusions about the future cases from a current sample), causal inference (concluding that association implies causality), and Bayesian inference (given new evidence [data], using probability theory [Bayes’ theorem] to alter belief in a hypothesis).

All inductive arguments contain multiple premises that provide grounds for a conclusion but do not necessitate it (in contrast to a deductive argument where the premises, if true, entail the conclusion). In other words, a conclusion drawn from an inductive argument is probable (at best), even if its premises are correct. For this reason, all inductive arguments, while ampliative, are considered to be logically invalid and are judged, instead, according to their “strength” (i.e., whether they are “inductively strong” or “inductively weak”). The strength of an inductive generalization is determined by the number of observations supporting it and the extent to which the observations reflect all observations that could be made. The more (consistent) observations that exist, the more likely the conclusion is correct (inconsistent observations, of course, reduce the argument’s inductive strength). The typical form of an inductive generalization is given below:

(All As I have observed are Bs)

∴ All As are Bs

Like deductive arguments, inductive generalizations can be categorical, that is, represent conclusions about “all” (as above), “no,” or “some” members of a class, or they may involve quantitative arguments, for example, “50% of all coins I have sampled are quarters; therefore, 50% of all coins coming from the same lot that I have sampled probably are quarters” (or, as a clinical example, “30% of the patients I have examined are obese; therefore, 30% of patients sampled from the same population as those who I have examined probably are obese”).

Not all inductive hypotheses used by scientists have been formulated by scientists; some, in fact, owe their origin to folklore. For example, by the late eighteenth century, it was common knowledge among English farm workers that when humans were exposed to cows infected with cowpox (vaccinia), they became immune to its more severe human analogue, smallpox. The English surgeon, Edward Jenner (1749–1823), used this “hypothesis” as the basis of a series of scientific experiments, using exudates from an infected milkmaid, to develop and formally test a vaccine against this disease [ 11 ]. He became famous for using vaccination as a method for preventing infection, though there is growing recognition that the first successful inoculations against smallpox actually were performed by a farmer, Benjamin Jesty, some 20 years earlier, who vaccinated his family using cowpox taken directly from a local cow [ 12 ]. It also has been claimed that Charles Darwin used inductive reasoning when generalizing about the shapes of the beaks from finches from the various Galapagos Islands [ 13 ] and when forming conjectures from observations based on the breeding of dogs, pigeons, and farm animals at home (inferences that formed underpinnings of his theory of evolution) and that Gregor Mendel used the same form of reasoning to conceptualize his “law of hybridization” [ 14 ]. Even if these claims are true (and there is far from universal agreement on this matter), inductive generalizations typically are regarded as inferior to hypothesis-generating methods that involve more theoretical reasoning, that consider variations in circumstances (i.e., possible confounding factors) that may account for spurious patterns, and that provide possible causal explanation for observed phenomena. Moreover, recent research in cognition and the relatively new field of neural modeling suggest that simple induction “across a limited set of observations” may have a far smaller role in scientific reasoning than previously realized [ 15 ].

Hypothesis by Abduction

Of the three primary methods of reasoning, the one that has been most implicated in the creation of novel ideas, including scientific discoveries, is the logical process of abduction (from the Latin ab [meaning “away from”] and dūcerė [“to draw or to lead”]). It also is the most common mode of reasoning employed by clinicians when making diagnostic inferences. Abduction was introduced into modern logic by American philosopher and mathematician, Charles Sanders Peirce (1839–1914) [ 16 ], and remains an important, albeit controversial, topic of research among philosophers of science and students of artificial intelligence. It refers to the process of formulation and acceptance on probation of a hypothesis to explain a surprising observation. Thus, hypotheses formed by abduction (unlike those formed by induction) are always explanatory. (The reader should note that other synonyms for, and definitions of, abduction exist, e.g., “retroduction,” “reduction,” “inference to the best explanation,” etc., the latter reflecting the evaluative and selective functions that also have been associated with this term.) Abductive reasoning entails moving from a ­ consequent (the observation or current “fact”) to its antecedent (presumed cause or precondition) through a general rule. It is considered “backward” because the inference about the antecedent is drawn from the consequent .

Peirce devoted his earliest work (before 1900), as did Aristotle long before him, to furthering the development of syllogistic theory to express logical relations. During this early period, abduction (then termed by him as hypothesis ) was taken to mean the use of a known “rule” to explain an observation (“result”); accordingly, his initial efforts were devoted to demonstrating how the hypothesis relates to the premises of the argument and how it differs from the logical structure of other forms of reasoning (i.e., deduction or induction). In his essay, Deduction, Induction, Hypothesis , Peirce presents an abductive syllogism:

Rule: “All the beans from this bag are white.”

Result: “These beans are white.”

Case: “These beans are from this bag.” [ 16 ]

In this argument, the “rule” and “result” represent the premises (background knowledge and observation, respectively [the order is arbitrary]) and the “case” represents the conclusion (here, the hypothesis). Had this argument been expressed deductively, the “case” would have been the second premise, and the “result,” the conclusion (i.e., “all the beans from this bag are white, these beans are from this bag; therefore, these beans are white”). It should be obvious to the reader that the abductive argument is logically less secure than a deductive argument (or even an inductive argument). It represents a possible conclusion only (after all, the beans might come from some other bag—or from no bag at all). Therefore, like an inductive argument, it is ampliative though logically invalid. Its strength is based on how well the argument accounts for all available ­evidence, including that which is seemingly contradictory.

As Peirce’s work evolved, he shifted his efforts to developing a theory of inferential reasoning in which abduction was taken to mean the generation of new rules to explain new observations. In so doing, he focused on, what some have termed, the “creative character of abduction” [ 17 ]. Peirce argued that abduction had a major role in the process of scientific inquiry and, indeed, was the only inferential process by which new knowledge was created—a view that was, and continues to be, hotly debated by the philosophical community. In his later work, Peirce described the logical structure of abduction as follows:

The surprising fact, C, is observed.

But if A were true, C would be a matter of course.

Hence, there is reason to suspect that A is true. [ 18 ]

The “surprise” (the stimulus to the abductive inference) arises because the observation is viewed, at that moment in time, as an anomaly, given the observer’s preexisting corpus of knowledge (theory base) which cannot account for it. The lack of compatibility between the observation and expectation introduces a type of cognitive dissonance that seeks resolution through the adoption of a coherent explanation. In Peirce’s opinion, the explanation might be nothing more than a guess (Peirce believed that humans were “hardwired” with the ability for guessing correctly) that, unlike an inductive generalization, enters the mind “like a flash” [ 18 ] or, what is commonly termed, as a “eureka moment” or an “ah ha!” experience. Because a guess (insightful or not), by its very nature, is speculative (and, as noted above, is a relatively insecure form of reasoning), Peirce recognized that an abductive hypothesis must be rigorously tested before it could be admitted into scientific theory. This, he reasoned, is accomplished by using deduction to explicate the consequences of the hypothesis (i.e., the predictions) and induction to form a conclusion about the likelihood of their truthfulness, based on experimental verification. According to Peirce, these are the primary roles of deduction and induction in the scientific process. Figure 3.1 illustrates the Peircian view of the relation between abduction, deduction, and induction as interpreted by Flach and Kakas [ 19 ].

The three stages of scientific inquiry ( From Abduction and Induction. Essays on their Relation and Integration, Flach PA and Kakas AC. Abductive and Inductive Reasoning: Background and Issues, Chap. 1 , pp. 1–27, Copyright 2000, with permission from Klewer Academic Publishers )

Countless abductively derived hypotheses, principles, theories, and laws have been put forward in science. Many, if not most, owe to the serendipitous consequences of an unexpected observation made while looking for something else [ 20 ]. Well-known examples of such “happy accidents” include:

Archimedes’ principles of density and buoyancy

Hans Christian Oersted’s theory of electromagnetism

Luigi Galvani’s principle of bioelectricity

Claude Bernard’s neuroregulatory principle of circulation

Paul Gross’ protease-antiprotease hypothesis of pulmonary emphysema

Although, as Peirce points out, all three modes of inference (abduction, deduction, and induction) are used in the process of scientific inquiry, each requires different skills. As scholars have noted, deduction requires the capacity to reason logically and inductive reasoning requires understanding of the statistical implications of drawing conclusions from samples to populations. In contrast, as Danmark et al. have noted, abduction requires the “discernment of new relations and connections not immediately obvious” [ 21 ]—in other words, to “think outside the box.” For this reason, the best abductive hypotheses in science have been made by those who not only are observant, wise, and well grounded in their disciplines but who also are imaginative and receptive to new ideas. This view was, perhaps, best expressed by Louis Pasteur (1822–1895) when he argued, “In the fields of observation, chance favors only prepared minds” [ 22 ]. Accordingly, developing the “prepared mind,” in general, and enhancing the capacity to reason abductively, deductively, and inductively, in particular, should be among the most important goals of those seeking to effectively engage in the process of scientific discovery.

Characteristics of the Research Hypothesis

Irrespective of how it is formulated (or the problem or discipline for which it is formulated), a research hypothesis should fulfill the following five requirements:

It should reflect an inference about variables.

The purpose of any hypothesis is to make an inference about one or more variables. The inference can be as simple as predicting a single characteristic in a population (e.g., mean height, prevalence of lung cancer, incidence of acute myocardial infarction, or other population parameter) or, more commonly, it represents a supposition about an association between two or more variables (e.g., smoking and lung cancer, diet and hypertension, age and exercise tolerance, etc.). It is, therefore, important for the investigator to understand what is meant by a variable and how it functions in the setting of a hypothesis.

In its broadest sense, a variable is any feature, attribute, or characteristic that can assume different values (levels) within the same individual at different points in time or can differ from one member of the study population to another. Typical variables of interest to biomedical researchers include subject profile characteristics (e.g., age, weight, gender, ­etiology, stage of disease), nature, place, duration of naturally occurring exposures (e.g., risk factors, environmental influences) or purposively applied interventions, and subject outcomes or responses (e.g., morbidity, mortality, symptom relief, physiological, behavioral, or attitudinal changes) among others.

It is important to recognize that a characteristic that functions as a variable in one study does not necessarily serve as a variable in another. For example, if an investigator wished to determine the relation of gender to prevalence of diabetes, it would be necessary to study this problem in a group comprising males and females, some with and some without this disease. Because intersubject differences exist for both characteristics, gender and diabetes would be considered study variables, and a hypothesis could be constructed about their association. However, if all patients in a study group were women with diabetes, no hypothesis could be developed about the relation between gender and diabetes since these attributes would be invariable. (Fuller discussion of nature and role of variables, and their relation to the hypothesis, is presented later in this chapter.)

It should be stated as a grammatically complete, declarative sentence.

A hypothesis should contain, at minimum, a subject and predicate (the verb or verb phrase and other parts of the predicate modifying the verb). The statements “relaxation (subject) decreases (verb) blood pressure (object, or predicate noun),” “depression (subject) increases (verb) the rate of suicide (predicate),” and “consumption of diet cola (subject) is related to (verb phrase) body weight (object, or predicate noun)” are illustrative of hypotheses that meet this requirement. In these examples, the subject and predicate modifiers reflect the variables to be related, and the verb (or verb phrase) defines the nature of the expected association.

It should be expressed simply and unam­biguously.

For a hypothesis to be of value in a study, it must be clear in meaning, contain only one answer to any one question, and reflect only the essential elements of solution. The reason is that the hypothesis guides all subsequent research activities, including selection of the population and measurement instruments, collection and analysis of data, and interpretation of results. For example, the hypothesis “right ventricular performance is the best predictor of survival among patients with valvular heart disease, but is less important in others” would be difficult to validate. First, what is meant by right ventricular performance? Does this refer to ejection fraction at rest, at exercise, or the change from rest to exercise, or to some other parameter? Second, what is the meaning of “best”? Does it signify ease of measurement or does is it relate to the strength of statistical association? Third, to what is right ventricular performance compared? Is the contrast between right ventricular performance and clinical descriptors, anatomic descriptors, other functional descriptors, or between all of these? Fourth, what type of “valvular heart disease” is being studied? Is it regurgitant, stenotic, or both? Does it involve the mitral, aortic, or some other heart valve? Finally, what is meant by “less important”? Who (or what) are the “others”? As is true for the research problem, the clearer and less complex the statement of the hypothesis, the more straightforward the study and the more useful the findings.

It should provide an adequate answer to the research problem.

For a hypothesis to be adequate, it must address, in a satisfactory manner, both the content and scope of the central question; that is, whether the problem is narrow or broad, simple or complex, evaluation of the hypothesis(es) should result in the full resolution of the research problem. For this reason, it is recommended that the investigator formulate at least one hypothesis for every subproblem articulated in the study. Equally important, a hypothesis must be plausible; for this condition to be satisfied, the hypothesis should be based on prior relevant observation and experience, buttressed by consideration of existing theory, and should reflect sound reasoning and knowledge of the problem at hand. In contrast, speculations which have either no empirical support or legitimate theoretical basis, even if interesting, constitute poor hypotheses and typically yield weak or uninterpretable study outcomes. Finally, if the hypothesis is explanatory in nature (rather than an inductive generalization), all else being equal, it should represent the simplest of all possible competing explanations for the phenomenon or data at hand [ 23 ], a principle known as Occam’s razor or entia non sunt multiplicanda praeter necessitatem (Latin for “entities must not be multiplied beyond necessity”).

It should be testable.

A hypothesis must be stated in such a way as to allow for its examination which, in the biomedical and other empirical sciences, is achieved through the acts of observation or experimentation, analysis, and judicious interpretation. If one or more of the elements comprising the hypothesis is not present in the population or sample, or if a phenomenon or characteristic contained within the hypothesis is highly subjective or otherwise difficult to measure, the hypothesis cannot be properly evaluated. For example, the statement “female patients cope better with stress than male patients” would be a poor hypothesis if the investigator did not have access to both male and female patients or was unable to generate acceptable definitions and measures to evaluate “coping” and “stress.” An even more egregious example is the hypothesis “prognosis following diagnosis of ovarian cancer is related to the patient’s survival instinct,” as it would be extremely difficult to develop empirical data in support of a “survival instinct”—assuming it did exist.

For many years, philosophers of science have argued about what constitutes evidence in science or support for a scientific hypothesis. By the mid-twentieth century, the tenets of logical positivism (or logical empiricism) dominated the philosophy of science in the United States as well as throughout the English-speaking world [ 24 ], replacing the Cartesian emphasis on rationalism as a primary epistemological tool. Strongly eschewing metaphysical and theological explanations of reality, the logical positivists argued that a proposition held meaning only if it could be “verified” (i.e., if its truth could be determined conclusively by observable facts). Early critics of logical positivism, most notable among them Karl Popper, believed that “verifiability” was too stringent a criterion for scientific discovery. This, he argued, was due to the logical limitations inherent in inductive reasoning, namely, the deductive invalidity of forming a generalization based on the observation of particulars, and the attendant uncertainty of such an inference. Thus, while both positive existential claims (e.g., “there is at least one white swan”) and negative universal claims (e.g., “not all swans are white”) could be confirmed by finding, respectively, at last one white swan or one black swan, it would be impossible to verify a positive universal claim (e.g., all swans are white). To accomplish that, one would have to observe every swan in existence, at all times and in all places, or risk being wrong.

According to Popper, the hallmark of a testable claim is its capacity to be falsified [ 25 ]. In his view, falsification ( not verification) is the criterion for demarcation between those hypotheses, theories, and other propositions that are scientific versus those that are not scientific. This, of course, did not mean that a scientific hypothesis or theory must be false; rather, if it were false, it could be shown to be so. Returning to our earlier example, all that would be required to disprove the claim “all swans were white” is to find a swan that is not white. Indeed, this inductive inference, based on the observation of millions of white swans in Europe, was shown to be false when black swans were discovered in Western Australia in the eighteenth century [ 26 ]—an event that was not unnoticed by Popper. It provided clear support for his assertion that no matter how many observations are made that appear to confirm a proposition, there is always the possibility that an event not yet seen could refute it. Similarly, any scientific hypothesis, theory, or law could be falsified by finding a single counterexample.

Popper’s greatest contribution to science was his characterization of scientific inquiry, based on a cyclical system of conjectures and refutations (a form of critical rationalism) widely known as the “hypothetico-deductive method” [ 27 ]. A schematic of Popper’s view of this method is shown in Fig. 3.2 . Consistent with Popper’s writing on the subject, the terms hypothesis and theory are used interchangeably as both are viewed as tentative, though most workers in the field currently reserve the latter term for hypotheses (or related systems of hypotheses) that have received consistent and long-standing empirical support.

The hypothetico-deductive model: Popper’s view of the role of falsification in scientific reasoning

The reader will note that the hypothetico-deductive method begins with an early postulation of a hypothesis. The investigator then uses deductive logic to form predictions from the hypothesis that should be true if the hypothesis is, in fact, correct. The nature of the predictions can vary from study to study, but they share the common attribute of being unknown before data collection. The predictions are then evaluated by formal experimentation or observation. Assuming a properly designed study, those predictions that are discordant with data falsify the hypothesis, which is then discarded or revised, leading to additional study. Although a hypothesis can never be shown to be true via collection of compatible information (as Popper noted, a subsequent demonstration of counterfactual data can overturn any hypothesis), the extent to which it survives repeated attempts at falsification provides support (corroboration) for its validity. As a result, testing of a hypothesis serves to advance the existing theory base and body of knowledge. Popper argued that the hypothetico-deductive method was the only sound approach to scientific reasoning; moreover, in his opinion, it was the only method by which science made any progress.

Although Popper did not originate the hypothetico-deductive method, he was the first to explicate the central role of falsification versus confirmation of a hypothesis in the developing science. While his arguments have been criticized by other philosophers of science who assert that scientists do not necessarily reason that way [ 28 ], his views remain prominent in modern philosophy and continue to appeal to many modern scientists [ 29 ]. Today, the Popperian view of the hypothetico-deductive method, with its emphasis on testing to falsify a proposed hypothesis, generally is taken to represent an ideal (if not universal) approach to curbing excessive inductive speculation and ensuring scientific objectivity, and is considered to be the primary methodology by which biological knowledge is acquired and disseminated [ 30 ].

Types of Hypotheses

Hypotheses can be classified in several ways, as shown below.

Conceptual Versus Operational Hypotheses

Hypotheses can vary according to their degree of specificity or precision and theoretical relatedness. Hypotheses can be written as broad or general statements, in which case they are termed conceptual hypotheses . For example, an investigator may hypothesize that “a high-fat diet is related to severity of coronary artery disease” or another may conjecture that “depression is associated with a relatively high incidence of morbid events.” Although these may be important hypotheses, these statements cannot be directly tested as they are fundamentally abstract. What do the investigators mean by “high fat,” “depression,” “severity of coronary artery disease,” “relatively high,” or “morbid events”? How will these terms be evaluated?

To render conceptual hypotheses testable, they must be recast as more specific statements with elements (variables) that are precisely defined according to explicit observable or measurable criteria. Hypotheses of this type are referred to as operational hypotheses or, alternatively, specific hypotheses or predictions and represent the specific (observable) manifestation of the conceptual hypothesis that the study is designed to test. Once the study is designed, data will be collected and analyzed to determine whether they are concordant or discordant with the operational hypothesis which, ultimately, will be reinterpreted in terms of its broader meaning as a conceptual hypothesis. Figure 3.3 below illustrates a simplified version of the hypothetico-deductive method , as conceptualized by Kleinbaum, Kupper, and Morgenstern [ 31 ] depicting the relation of conceptual and operational hypotheses to the design and interpretation of the study.

Interrelation of conceptual hypotheses, operational hypotheses, and the hypothetico-deductive method (Reprinted with permission Kleinbaum DG, Kupper LL, Morgenstern H. Epidemiologic Research: Principles and Quantitative Methods, Fig. 2.2 : An Idealized Conceptualization of the Scientific Method (New York: Van Nostrand Reinhold 1982), p. 35)

Construction of operational hypotheses represents an important preliminary step in the development of the research design, data collection strategy, and statistical analysis plan and is described in greater detail in subsequent sections of this chapter.

Single Variable Versus Multiple Variable Hypotheses

Some investigations are undertaken to determine whether a mean, proportion, or other parameter from a sample varies from a specified value. For example, a group of obstetricians may have read a report that concludes that, throughout the nation, the average length of stay following uncomplicated caesarian section is 5 days. They may have reason to believe that the length of stay for similar patients at their institution differs from the national average and would like to know if their belief is correct. To study the question, they must first recast their question as a hypothesis including the stipulated variable, select a representative sample of patients from their institution, and compare data from their sample with the national average (stipulated value) using an appropriate one-sample statistical test. (The reader should note that the only variable being tested within this hypothesis is length of stay. In this case, caesarian section is only a descriptor of the target population because all data to be examined are from patients undergoing this procedure.)

However, the objective of most hypotheses is not to draw inferences about population parameters but to facilitate evaluation of a proposition that two or more variables are systematically related in some manner [ 32 ]. Indeed, some methodologists recognize only the latter form of argument as a legitimate hypothesis [ 7 , 33 – 35 ]. The simplest hypotheses about intervariable association contain two variables ( bivariable hypotheses ), for example:

Caffeine consumption is more frequent among smokers than nonsmokers.

Women have a higher fat-to-muscle ratio than men.

Heart attacks are more common in winter than in other seasons.

If the objective of the study is to compare the relative association of several characteristics, it usually will be necessary to construct a single hypothesis which relates three or more variables ( multivariable hypotheses ), for example:

Ischemia severity is a stronger predictor of cardiac events than symptom status and risk factor score.

Response to physical training is affected more by age than gender.

Improvement in health-related quality of life after cardiac surgery is influenced more by preoperative symptoms than by ventricular performance or geometry.

The number and type of variables contained within the hypothesis (as well as the nature of the proposed association) will dictate the study design, measurement procedures, and statistical analysis of the results. These concepts are addressed in Chaps. 5 and 11 .

Hypotheses of Causality Versus Association or Difference

The relation posited between variables may be cast as one of cause-and-effect , in which case the researcher hypothesizes that one variable affects or influences the other(s) in some manner. For example:

Estrogen produces an increase in coronary flow.

Smoking promotes lung cancer.

Patient education improves compliance.

Coronary artery bypass grafting causes a reduction in the number of subsequent cardiac events.

However, hypotheses often are not written this way because support for a cause-and-effect relation requires not only biological plausibility and a strong statistical result but also an appropriate (and usually rigorous) study design. If the investigator believes that the variables are related, but prefers not to speculate on the influence of one variable on another, the hypothesis may be cast to propose an association only, without explicit reference to causality. For example:

Surgical benefit is related to preoperative ischemia severity.

Exercise tolerance is correlated with chronological age.

Consumption of low-calorie beverages is associated with body weight.

Finally, hypotheses also can be written to a assert that there will be a difference between levels of a variable among two or more groups of individuals or within a single group of individuals at different points in time, as shown by the following examples:

Patients enrolled in a health maintenance organization (HMO) will have a different number of hospitalizations than those enrolled in “preferred provider organizations (PPOs)” or traditional “fee-for-­service” insurance plans.

Among patients undergoing mitral valve repair or replacement, left ventricular performance will be dissimilar at 1 versus 3 years after operation.

The hypothesis also can be framed so that the nature of the association (e.g., linear, curvilinear, positive, inverse, etc.) or difference (“larger” or “smaller,” “better” or “poorer,” etc.) will be specified (see below, Alternative hypotheses [directional]).

Mechanistic Versus Nonmechanistic Hypotheses

Hypotheses can be written so as to provide a mechanism (i.e., an explanation) for an asserted relationship or prediction, or they can be written without defining an underlying mechanism. Mechanistic hypotheses are common in preclinical research which typically attempts to define biochemical and physiological causes of disease or dysfunction and pathways amenable to therapeutic intervention.

Shown below are two examples of mechanistic hypotheses that were evaluated in two different preclinical investigations: (Note the use of the phrase “as a result of” in the first hypothesis evaluating the impact of endothelial nitric oxide synthase [eNOS] and “due to” in the second hypothesis evaluating antagonism of endothelin [ET]-induced inotropy. Italics have been added for emphasis.)

“Gender-specific protection against myocardial infarction occurs in adult female as compared to male rabbits as a result of eNOS upregulation” [ 36 ].

“ET-induced direct positive inotropy is antagonized in vivo by an indirect cardiodepressant effect due to a mainly ETA-mediated and ET-induced coronary constriction with consequent myocardial ischemia” [ 37 ].

In clinical research, hypotheses more commonly are nonmechanistic (i.e., framed without including an explicit explanation). Shown below are two published literature examples:

“Patients with medically unexplained symptoms attending the clinic of a general adult neurologist will have delayed earliest and continuous memories compared with patients whose symptoms were explained by neurological disease” [ 38 ].

“Patients with acute mental changes will be scanned more frequently than other elder patients” [ 39 ].

The reader will note that these hypotheses do not include the mechanism for memory variations in these patient populations (first example) or the reasons why elderly patients with acute mental changes should be scanned more frequently than comparable patients without such changes (second example). In situations like this, it is critical that the justification be clear from the introductory section of the research paper or protocol.

Alternative Versus Null Hypotheses

The requirement that a hypothesis should be capable of corroboration or unsupportability (“falsification”) reflects the fact that two ­outcomes always can arise out of a study of any single research problem. Thus, prior to collecting and evaluating empirical evidence to resolve a problem, the investigator will posit two opposing assertions. The first assertion will indicate the supposition for which support actually is sought (e.g., that there is a difference between a population parameter and an expected value or, more commonly, that there is some form of relation between variables within a particular population); the other will indicate that there is no support for this supposition. This first type of assertion is termed the alternative hypothesis and is generally denoted H A or H 1 . The alternative hypothesis can be differentiated further according to its quantitative attributes. As an example, in a study evaluating the impact of beta-adrenergic antagonist treatment (β-blockade) on the incidence of recurrent myocardial infarctions (MIs), an investigator could frame three contrasting alternative hypotheses:

The proportion of recurrent MIs among comparable patients treated with versus without β-blockade is different.

The proportion of recurrent MIs among patients treated with β-blockade is less than that among comparable patients treated without β-blockade.

The proportion of recurrent MIs among patients treated with β-blockade is greater than that among comparable patients treated without β-blockade.

The first of these statements is termed a nondirectional hypothesis because the nature of the expected relation (i.e., the direction of the intergroup difference in the proportion of recurrent infarctions) is not specified. The second and third statements are termed directional hypotheses since, in addition to positing a difference between groups, the nature of the expected difference (positive or negative) is predefined. Generally, the decision to state an alternative hypothesis in a directional versus nondirectional manner is based on theoretical considerations and/or the availability of prior empirical information. (In statistics, a nondirectional hypothesis is usually referred to as a two-tailed or two-sided hypothesis; a directional hypothesis is referred to as a one-tailed or one-sided hypothesis.)

As noted, the hypothesis reflects a tentative conjecture which, to gain validity, ultimately must be substantiated by experience (empirical evidence). However, even objectively measured experience varies from time to time, place to place, observer to observer, and subject to subject. Thus, it is difficult to know whether an observed difference or association was produced by random variation or actually reflects a true underlying difference or association in the population of interest. To deal with the problem of uncertainty, the investigator must implicitly formulate and test what, in essence, is the logical opposite of his or her alternative hypothesis (i.e., that the population parameter is the same as the expected value or that the variables of interest are not related as posited). Thus, the investigator must attempt to set up a straw man to be knocked down. This construct (which need not be not stated in the research report), is termed a null (or no difference) hypothesis and is designated H 0 . A null hypothesis asserts that any observable differences or associations found within a population are due to chance and is assumed true until contradicted by empirical evidence. In the single variable (one-sample) hypothesis, the assertion is that the parameter of interest is not different from some expected population value, whereas in a bivariable or multivariable hypothesis, the assertion is that the variables of interest are un related to some factor or to each other.

A null hypothesis is framed by inserting a negative modifier into the statement of the alternative hypothesis. In the examples given above, the following null statements could be developed:

The proportion of recurrent MIs among comparable patients treated with versus without β-blockade is not different.

The proportion of recurrent MIs among patients treated with β-blockade is not less than that among comparable patients treated without β-blockade.

The proportion of recurrent MIs among patients treated with β-blockade is not greater than that among comparable patients treated without β-blockade.

Only after both the null and alternative hypotheses have been specified, and the data collected, can an appropriate test of statistical significance be performed. If the results of statistical analysis reveal that chance is an unlikely explanation of the findings, the null hypothesis is rejected and the alternative hypothesis is accepted. Under these circumstances, the investigator can conclude that there is a statistically significant relation between the variables under study (or a statistically significant difference between a parameter and an expected value). On the other hand, if chance cannot be excluded as a probable explanation for the findings, the null, rather than the alternative, hypothesis must be accepted. It is important to note that acceptance of the null hypothesis does not mean that the investigator has demonstrated a true lack of association between variables (or equation between a population parameter and an expected value) any more than a verdict of “not guilty” constitutes proof of a defendant’s innocence in a legal proceeding. Indeed, in criminal law, such a verdict means only that the prosecution, upon whom the burden of proof rests, has failed to provide sufficient evidence that a crime was committed. Similarly, in research, failure to overturn a null hypothesis (particularly when the alternative hypothesis has been argued) generally is taken to mean that the investigator, upon whom the burden of “proof” (or, more appropriately, corroboration) also rests, has failed to demonstrate the expected difference or association. Null results may reflect reality, but they may also be due to measurement error and inadequate sample size. For this reason, negative studies , a term for research that yields null findings, are far less likely to gain publication than studies that demonstrate a statistically significant association [ 40 , 41 ]. (See Chap. 9 for a more detailed discussion of “publication bias.”)

Constructing the Hypothesis: Differentiating Among Variables

As indicated earlier, hypotheses most commonly entail statements about variables. Variables, in turn, can be differentiated according to their level of measurement (or scaling characteristics) or the role that they play in the hypothesis.

Level of Measurement

Variables can be classified according to how well they can be measured (i.e., the amount of information that can be obtained in a given measurement of an attribute). One factor that determines the informational characteristics of a variable is the nature of its associated measurement scale, that is, whether it is nominal, ordinal, interval, or ratio—a classification system framed in 1946 by Stevens [ 42 ]. Understanding these distinctions is important because scaling characteristics influence the nature of the statistical methods that can be used for analyzing data associated with a variable.

The Nominal Variable

Nominal variables represent names or categories. Examples include blood type, gender, marital status, hair color, etiology, and presence versus absence of a risk factor or disease, and vital status. Nominal variables represent the weakest level of measurement as they have no intrinsic order or other mathematical properties and allow only for qualitative classification or grouping. Their lack of mathematical properties precludes calculation of measures of central tendency (such as means, medians, or modes) or dispersion. When all variables in a hypothesis are nominal, this limits the types of statistical operations that can be performed to tests involving cross-classification (e.g., tests of differences between proportions). Sometimes, variables that are on an ordinal, interval, or ratio scale are transformed into nominal categories using cutoff points (e.g., age in years can be recoded into old versus young; height in meters to tall versus short; left ventricular ejection fraction in percent to normal versus subnormal).

The Ordinal Variable

Ordinal variables are considered to be semiquantitative. They are similar to nominal variables in that they are comprised of categories, but their categories are arranged in a meaningful sequence (rank order), such that successive values indicate more or less of some quantity (i.e., relative magnitude). Typical examples of ordinal variables include socioeconomic status, tumor classification scores, New York Heart Association (NYHA) functional class for angina or heart failure, disease severity, birth order, perceived level of pain, and all opinion survey scores. However, distances between scale points are arbitrary. For example, a patient categorized as NYHA functional class IV may have more symptomatic debility than one categorized as functional class II, but he or she does not necessarily have twice as much debility; indeed, he or she may have considerably more than twice as much debility. Appropriate measures of central tendency for ordinal variables are the mode and median (rather than the mean or arithmetic average) or percentile. Similarly, hypothesis tests of subgroup differences based on ordinal outcome variables are limited to nonparametric approaches employing analysis of ranks or sums of ranks.

The Interval Variable

Interval variables, like ratio variables (below), are considered quantitative or metric variables because they answer the question “how much?” or “how many?” Both may take on positive or negative values. A common example of an interval variable is temperature on a Celsius or Fahrenheit scale. Both interval and ratio variables provide more precise information than ordinal variables because the distances between successive data values represent true, equal, and meaningful intervals. For example, the difference between 70 ° F and 80 ° F is equivalent to the difference between 80 ° F and 90 ° F. However, the zero point on an interval scale is arbitrary (note, freezing on a Celsius scale is 0 ° but is 32 ° on a Fahrenheit scale) and does not necessarily connote absence of a property (in this case, absence of kinetic energy). When analyzing interval data, one can add or subtract but not multiply or divide. Most statistical and operations are permissible, including calculation of measures of central tendency (e.g., mean, median, or mode), measures of dispersion (e.g., standard deviation, standard error of the mean, range), and performance of many statistical tests of hypotheses including correlation, regression, t-tests, and analysis of variance. However, due to the absence of a true zero point, ratios between values on an interval scale are not meaningful (though ratios of differences can be computed).

The Ratio Variable

Like interval variables, the distances between successive values on a ratio scale are equal. However, ratio variables reflect the highest level of measurement because they contain a true, nonarbitrary zero point that reflects complete absence of a property. Examples of ratio variables include temperature on a Kelvin scale (where zero reflects absence of kinetic energy), mass, length, volume, weight, and income. When ratio data are analyzed, all arithmetic operations are available (i.e., addition, subtraction, multiplication, and division). The same statistical operations that can be performed with interval variables can be performed with ratio variables. However, ratio variables also permit meaningful calculation of absolute and relative (or ratio) changes in a variable and computation of geometric and harmonic means, coefficients of variation, and logarithms.

Quantitative variables (interval or ratio) can be either continuous or discrete. Continuous variables (e.g., weight, height, temperature) differ from discrete variables in that the former may take on any conceivable value within a given range, including fractional values or decimal values. For example, within the range 150–151 lbs, an individual theoretically can weigh 150 lbs, 150.5 lbs or 150.95 lbs, though the capacity to distinguish between these values clearly is limited by the precision of the measurement device. In contrast, discrete variables (e.g., number of dental caries, number of white cells per cubic centimeter of blood, number of readers of medical journals, or other count-based data) can take on only whole numbers. Nominal and ordinal variables are intrinsically discrete, though in some disciplines (e.g., behavioral sciences), ordinally scaled data often are treated as continuous variables. This practice is considered reasonable when ordinal data intuitively represent equivalent intervals (e.g., visual analogue scales), when they contain numerous (e.g., 10 or more) possible scale values or “orderings” [ 43 ], or when shorter individual measurement scales are combined to yield summary scores. The reader should note, however, that in other disciplines and settings, treating all data as continuous data is controversial and generally is not ­recommended [ 44 ].

Role in the Research Hypothesis

Another method of classifying variables is based on the specific role (function) that the variable plays in the hypothesis. Accordingly, a variable can represent (1) the putative cause (or be associated with a causal factor) that initiates a subsequent response or event, (2) the response or event itself, (3) a mediator between the causal factor and its effect, (4) a potential confounder whose influence must be neutralized, or (5) an explanation for the underlying association between the hypothesized cause and effect. Viewed this way, variables may be independent, dependent, or may serve as moderator, control, or intervening variables. Understanding these distinctions is crucial for constructing a research design, executing a statistical program, or communicating effectively with a statistician.

The Independent Variable

The independent variable is that attribute within an individual, object, or event which affects some outcome. The independent variable is conceptualized as an input in the study that may be manipulated by the investigator (such as a treatment in an experimental study) or reflect a naturally occurring risk factor. In either case, the independent variable is viewed as antecedent to some outcome and is presumed to be the cause, or a predictor of that outcome, or a marker of a causal agent or risk factor. We call this type of variable “ independent ” because the researcher is interested only on its impact on other variables in the study rather than the impact of other variables on it. Independent variables are sometimes termed factors and their variations are called levels .

If, for example, if an investigator were to conduct an observational study of the effects of diabetes mellitus on subsequent cardiac events, the independent variable (or factor) would be history of diabetes, and its variants (positive or negative history) would be levels of the factor. As a second example, in an intervention study examining the relative impact of inpatient versus outpatient counseling on patient morbidity after a first MI, the independent variable (factor) would be the counseling, and its variants (inpatient counseling vs. outpatient counseling) would correspond to the alternative levels of the factor. The reader should note that in both of these hypothetical examples, there was only one independent variable (or factor) and that each factor had two levels. It is possible and, in fact, common for studies to have several independent variables and for each to have multiple factor levels (indeed, the number of factor levels in dose–response studies is potentially infinite). Care needs to be exercised as researchers often confuse a factor with two levels for two factors. Levels are always components of the factor. Understanding this distinction is essential for conducting statistical tests such as analysis of variance (ANOVA).

The Dependent Variable

In contrast to the independent variable, the dependent variable is that attribute within an individual or its environment that represents an outcome of the study. The dependent variable is sometimes called a response variable because one can observe its presence, absence, or degree of change as a function of variation in the independent variable. Therefore, the dependent variable is always a measure of effect .

As an example, suppose that an investigator wished to study the effects of adrenal ­corticosteroid therapy on systolic performance among patients with heart failure. In this study, systolic performance would be the dependent variable; the investigator would measure its degree of improvement or deterioration in response to introducing versus not introducing steroid treatment. Because it is a measure of effect, the dependent variable can be observed and measured but, unlike the independent variable, it can never be manipulated.

Independent and dependent variables are relatively simple to identify within the context of a specific investigation, for example, a prospective cohort or an experimental study or a well-designed retrospective study in which one variable clearly is an input, the second is a response or effect, and an adequately defined temporal interval exists between their appearance. However, when research is cross-­sectional, and variables merely are being correlated, it is sometimes difficult or impossible to infer which is independent and which is dependent. Under these circumstances, variables are often termed “covariates.”

The Moderator Variable

Often, an independent variable does not affect all individuals in the same way, and an investigator may have reason to believe that some other variable may be involved. If he or she wishes to systematically study the effect of this other variable, rather than merely neutralize it, it may be introduced into the study design as a moderator variable (also known as an “effect modifier”). The term moderator variable refers to a secondary variable that is measured or manipulated by the investigator to determine whether it alters the relationship between the independent variable of central interest and the dependent (response) variable. The moderator variable may be incorporated into a multivariate statistical model to examine its interactive effects with the independent variable or it may be used to provide a basis for stratifying the sample into two or more subgroups within which the effects of the independent variable may be examined separately.

For example, suppose a psychiatrist wishes to study the effects of a new amphetamine-type drug on task persistence in patients with attention deficit hyperactivity disorder (ADHD) who have not responded well to current medical therapy. She believes that the drug may have efficacy but suspects that its effect may be diminished by the comorbidity of chronic anxiety. Rather than give the new drug to patients with ADHD who do not also have anxiety and placebo to patients with ADHD plus anxiety, to avoid confounding, she enrolls both types of patients, randomly administers drug or placebo to members of each subgroup, and measures task persistence among all subjects at a fixed interval after onset of therapy. In this hypothetical study, the independent variable would be type of therapy (factor levels: new drug, placebo), the dependent variable would be task persistence, and chronic anxiety (presence, absence) would be the moderator. Figure 3.4 illustrates the importance of a moderator variable. If none had been used in the study, the data would have led the investigator to conclude that the new drug was ineffective as no overall treatment effect would have been observed for the ADHD group (left panel, diagonal patterned bar), with change in task persistence for the entire treated group similar to subjects on placebo (right panel). However, as noted, the new drug was not ineffective but instead was differentially effective, promoting greater task persistence among patients without associated anxiety but decreasing task persistence among those with anxiety, as hypothesized.

A hypothetical example of the effects of a moderator variable: influence of chronic anxiety on the impact of a new drug for patients with attention deficit hyperactivity disorder

A cautionary note is in order. Although moderator variables can increase the yield or accuracy of information from a study, an investigator needs to be very selective in using them as each additional factor introduced into the study design increases the sample size needed to enable the impact of these secondary factors to be satisfactorily evaluated. During the study planning process, the investigator must determine the likelihood of a potential interaction, the theoretical or practical knowledge to be gained by discovery of an interaction, and decide whether sufficient resources exist for such evaluation.

The Control Variable

In this last example, the investigator chose to evaluate the interactive effects of a secondary variable on the relation of the independent and dependent variables. Others in similar situations might choose not to study a secondary independent variable, particularly if it is viewed as extraneous to the primary hypothesis or focus of the study. Additionally, it is impractical to examine the effects of every ancillary variable. However, extraneous variables cannot be ignored because they can confound study results and render the data uninterpretable. Variables such as these usually are treated as control variables.

A control variable is defined as any potentially confounding aspect of the study that is manipulated by the investigator to neutralize its effects on the dependent variable. Common control variables are age, gender, clinical history, comorbidity, test order, etc. In the hypothetical example given above, if the psychiatrist had wanted to control for associated anxiety and not evaluate its interactive effects, she could have chosen patients with similar anxiety levels or, had his or her study employed a parallel design (which it did not), she could have made certain that different treatment groups were counterbalanced for that variable.

The Intervening Variable

Just as the moderator variable defines when (under what conditions) the independent variable exerts its action on the dependent variable, the “intervening variable” may help explain how and why the independent and dependent variables are related. This can be especially important when the association between independent and dependent variables appears ambiguous. There is general consensus that the intervening variable underlies, and accounts for, the relation between the independent and dependent variable. However, historically, workers in the field have defined them in different (and often contradictory) ways [ 45 ]. For example, Tuckman describes the intervening variable as a hypothetical internal state (construct) within an individual (motivation, drive, goal orientation, intention, awareness, etc.) that “theoretically affects the observed phenomenon but cannot be seen, measured, or manipulated; its effect must be inferred from the effects of the independent and moderator variables on the observed phenomenon” [ 35 ]. In the previous hypothetical example which examined the interactive effects of drug treatment and anxiety on task persistence, the intervening variable was attention . In educational research, the intervening variable between an innovative pedagogical approach and the acquisition of new concepts or skills is the learning process impacted by the former. In clinical or epidemiological research, the intervening variable can represent a disease process or physiological parameter that links an exposure or purposively applied intervention to an outcome (e.g., secondhand smoking causes lung cancer by inducing lung damage ; valvular surgery increases LV ejection fraction by improving contractility .). Others such as Baron and Kenny [ 46 ] view an intervening variable as a factor that can be measured (directly or by operational definitions, described later in this chapter), fully derived (“abstractable”) from empirical findings (data), and statistically ­analyzed to demonstrate its capacity to mediate the relation between the independent and dependent variables. As an example, Williamson and Schulz [ 47 ] measured and evaluated the relation between pain, functional disability, and depression among patients with cancer. They determined that the observed relation of pain to depression was due to diminution of function, operationally defined as activities of daily living (the intervening or mediating variable), which, in turn, caused depression. Similarly, Song and Lee [ 48 ] found that depression mediated the relation of sensory deficits (the independent variable in their study) to functional capacity (their dependent variable) in the elderly. (For a comprehensive discussion of mediation and statistical approaches to test for mediation, the reader is referred to MacKinnon 2008 [ 49 ].) Whether viewed as a hypothetical construct or as a measurable mediator, an intervening variable is always intermediate in the causal pathway by which the independent variable affects the dependent variable and is useful in explaining the mechanism linking these variables and, potentially, for suggesting additional interventions.

Below are two hypotheses from cardiovascular medicine in which constituent variables have been analyzed and labeled according to their role in each hypothesis.

Hypothesis 1 : “Among patients with heart failure who have similar clinical histories, those receiving adrenal corticosteroid treatment will demonstrate a greater improvement in systolic performance than those not receiving steroid treatment.”

Independent variable : adrenal corticosteroid treatment

Factor levels: 2 (treatment, no treatment)

Dependent variable : systolic performance

Control variable : clinical history

Moderator variable : none

Intervening variable : change in magnitude of the inflammatory process

Hypothesis 2 : “Patients with angina who are treated with β-blockade will have a greater improvement in their capacity for physical activity than those of the same sex and age who are not treated with β-blockade; this improvement will vary as a function of severity of initial symptoms.”

Independent variable : β-blockade treatment

Factor levels : 2 (treatment, no treatment)

Dependent variable : capacity for physical activity

Moderator variable: severity of initial symptoms

Control variables : sex and age

Intervening variable : alteration in myocardial work

In sum, many research designs, particularly those intended to test hypotheses about cause or prediction and effect, contain independent, dependent, control, and intervening variables. Some also contain moderator variables. Figure 3.5 illustrates their interrelationship.

Interrelation among variables in a study design

Role of Operational Definitions

As indicated earlier, one of the characteristics of a hypothesis that sets it apart from other types of statements is that it is testable . The hypotheses discussed thus far are conceptual. A conceptual hypothesis cannot be directly tested unless it is transformed into an operational hypothesis. To accomplish this, operational definitions must be developed for each element specified in the hypothesis.

An operational definition identifies the observable characteristics of that which is being studied. Its use imparts specificity and precision to the research, enabling others to understand exactly how the hypothesis was tested. As a corollary, it enables the scientific community to evaluate the appropriateness of the methodology selected for studying the problem. Operational definitions are required because a concept, object, or situation can have multiple interpretations. While double entendre is one basis of Western humor, inconsistent (or vague) definitions within a study are not comical as they typically lead to confused findings (and readers). Imagine, for example, what might occur if one member of an investigative team, studying the relative impact of two procedures for treating hemodynamically important coronary artery disease, defined “important” as >50% luminal diameter narrowing of one or more ­coronary vessels and another, working in the same study, defined it as ≥70% luminal diameter narrowing; or if one investigator studying new onset angina used 1 week as the criterion for “new” and another used 1 month. Operational definitions can describe the manipulations that the investigator performs (e.g., the intervention), or they can describe behaviors or responses. Still others describe the observable characteristics of objects or individuals. Once the investigator has selected appropriate operational definitions (this choice is entirely study dependent), all hypotheses in the study can be “operationalized.”

A hypothesis is rendered operational when its broadly (conceptually) stated variables are replaced by operational definitions of those variables. Hypotheses stated in this manner are called operational hypotheses , specific hypotheses , or predictions .

Let us consider two hypotheses previously given in this chapter:

“Patients with heart failure who are treated with adrenal corticosteroids will have better systolic performance than those who are not” is sufficiently general to be considered a conceptual hypothesis and, as such, is not directly testable. To render this hypothesis testable, the investigator could operationally define its constituent elements as follows:

Heart failure  =  “secondary hypodynamic cardiomyopathy”

Adrenal corticosteroids  =  “cortisol”

Better systolic performance  =  “higher left ventricular ejection fractions at rest”

The hypothesis, in its operational form, would state: “Patients with secondary hypodynamic cardiomyopathy who have received cortisol will have higher ventricular ejection fractions at rest than those who have not received cortisol treatment.”

Similarly, the hypothesis that “patients with angina who are treated with β-blockers will have a greater improvement in their capacity for physical activity than those not treated with β-blockers, and that this improvement will vary as a function of initial symptoms,” while complex, is still ­general enough to be considered conceptual. To render this hypothesis testable, its constituent elements could be defined as follows:

β-blockers  =  “propranolol” (assuming that the investigator was specifically interested in this drug)

Capacity for physical activity  =  “New York Heart Association functional class”

Severity of symptoms  =  angina class 1–2 ­versus angina class 3–4

This hypothesis, in its operational form, would be stated: “Patients with angina who are treated with propranolol will have greater improvement in New York Heart Association functional class than those not treated with propranolol, and this improvement will vary as a function of initial angina class (1–2 vs. 3–4).” In this form, the hypothesis could be directly tested, although the investigator would still need to specify measurement criteria and develop an appropriate design.

Any element of a hypothesis can have more than one operational definition and, as noted, it is the investigator’s responsibility to select the one that is most suitable for his or her study. This is an important judgment because the remaining research procedures (i.e., specification of subject inclusion/exclusion criteria, the nature of the intervention and outcome measures, and data analysis methodology) are derived from operational hypotheses. Investigators must be careful to use a sufficient number of operational definitions so that reviewers will have a basis upon which to judge the appropriateness of the methodology outlined in submitted grant proposals and manuscripts, so that other investigators will be able to replicate their work, and so that the general readership can understand precisely what was done and have sufficient information to properly interpret findings.

Once operational definitions have been developed and the hypothesis has been restated in operational form, the investigator can conduct the study. The next step will be to select a research design that can yield data to support optimal statistical hypothesis testing. The strengths, weaknesses, and requirements of various study designs will be discussed in Chaps. 4 and 5 .

Take-Home Points

A hypothesis is a logical construct, interposed between a problem and its solution, which represents a proposed answer to a research question. It gives direction to the investigator’s thinking about the problem and, therefore, facilitates a solution.

There are three primary modes of inference by which hypotheses are developed: deduction (reasoning from a general propositions to specific instances), induction (reasoning from specific instances to a general proposition), and abduction (formulation/acceptance on probation of a hypothesis to explain a surprising observation).

A research hypothesis should reflect an inference about variables; be stated as a grammatically complete, declarative sentence; be expressed simply and unambiguously; provide an adequate answer to the research problem; and be testable.

Hypotheses can be classified as conceptual versus operational, single versus bi- or multivariable, causal or not causal, mechanistic versus nonmechanistic, and null or alternative.

Hypotheses most commonly entail statements about “variables” which, in turn, can be classified according to their level of measurement (scaling characteristics) or according to their role in the hypothesis (independent, dependent, moderator, control, or intervening).

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Supino, P.G. (2012). The Research Hypothesis: Role and Construction. In: Supino, P., Borer, J. (eds) Principles of Research Methodology. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-3360-6_3

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Research Hypothesis: Elements, Format, Types

When a proposition is formulated for empirical testing, we call it a hypothesis. Almost all studies begin with one or more hypotheses.

Let’s Understand Research Hypothesis.

What is a hypothesis.

A hypothesis, specifically a research hypothesis, is formulated to predict an assumed relationship between two or more variables of interest.

If we reasonably guess that a relationship exists between the variables of interest, we first state it as a hypothesis and then test it in the field.

Hypotheses are stated in terms of the particular dependent and independent variables that are going to be used in the study.

Research Hypothesis Definition

A research hypothesis is a conjectural statement, a logical supposition, a reasonable guess, and an educated prediction about the nature of the relationship between two or more variables that we expect to happen in our study.

Unless you are creating an exploratory study, your hypothesis should always explain what you expect to happen during your experiment or research.

Remember, a hypothesis does not have to be correct. While the hypothesis predicts what the researchers expect to see, the research aims to determine whether this guess is right or wrong.

When experimenting, researchers might explore different factors to determine which ones might contribute to the outcome.

In many cases, researchers may find that the results of an experiment do not support the original hypothesis. When writing up these results, the researchers might suggest other options that should be explored in future studies.

Elements of a Good Hypothesis

Regardless of the type of hypothesis, the goal of a good hypothesis is to help explain the focus and direction of the experiment or research. As such, a good hypothesis will

• State the purpose of the research.
• Identify which variables are to be used.

A good hypothesis;

• Needs to be logical.
• Must be precise in language.
• It should be testable with research or experimentation.

A hypothesis is usually written in a form where it proposes that if something is done, then something will occur.

Finally, when you are trying to come up with a good hypothesis for your research or experiments, ask yourself the following questions:

• Is your hypothesis based on any previous research on a topic?
• Can your hypothesis be tested?
• Does your hypothesis include independent and dependent variables?

Before you come up with a specific hypothesis, spend some time doing background research on your topic.

Once you have completed a literature review, start thinking of potential questions you still have. Pay attention to the discussion section in the journal articles you read. Many authors will suggest questions that still need to be explored.

Basic Format of a Good Hypothesis

A hypothesis often follows a basic format of “If {this happens}, then {this will happen}.” One way to structure your hypothesis is to describe what will happen to the dependent variable if you change the independent variable.

The basic format might be:

“If {these changes are made to a certain independent variable}, then we will observe {a change in a specific dependent variable}.”

A few examples:

• Students who eat breakfast will perform better on a math test than students who do not eat breakfast.
• Students who experience test anxiety before an exam get higher scores than students who do not experience test anxiety.
• Drivers who talk on their mobile phones while driving will be more likely to make errors when driving than those who do not talk on the phone.
• People with high exposure to ultraviolet light will have a higher frequency of skin cancer than those who do not have such exposure.

Look at the last example.

Here is the independent variable (exposure to ultraviolet light)) is specified, and the dependent variable (skin cancer) is also specified.

Notice also that this research hypothesis specifies a direction in that it predicts that people exposed to ultraviolet light will have a higher risk of cancer.

This is not always the case. Research hypotheses can also specify a difference without saying which group will be better or higher than the other.

For example, one might formulate a hypothesis of the type: ‘Religion does not make any significant difference in the performance of cultural activities.’

In general, however, it is considered a better hypothesis if you can specify a direction.

Research hypotheses serve several important functions. The most important one is to direct and guide the research.

A few of the other functions of the research hypothesis are enumerated below:

• A research hypothesis indicates the major independent variables to be included in the study;
• A research hypothesis suggests the type of data that must be collected and the type of analysis that must be conducted to measure the relationship;
• A research hypothesis identifies facts that are relevant and that are not;
• A research hypothesis suggests the type of research design to be employed.

Types of Research Hypothesis

Two types of research hypotheses are;

• Descriptive hypothesis.
• Relational hypothesis.

Descriptive Hypotheses

Descriptive hypotheses are propositions that typically state some variables’ existence, size, form, or distribution.

These hypotheses are formulated in the form of statements in which we assign variables to cases.

For example,

• The prevalence of contraceptive use among currently married women in India exceeds 60%.

In this example, the case is ‘currently married women,’ and the variable is ‘prevalence of contraceptives.’ As a second example,

• The public universities are currently experiencing budget difficulties.

Here,’ public universities’ is the case, and ‘budget difficulties’ is the variable.

• The National Board of Revenue claims that over 15% of potential taxpayers falsify in their income tax returns.
• At most, 75% of the pre-school children in community A have a protein-deficient diet.
• The average sales in a superstore exceed taka 25 lac per month.
• Smoking increases the risk of lung cancer.
• The average longevity of women is higher among females than among males.
• Gainfully employed women tend to have lower than average fertility.
• Women with child loss experience will have higher fertility than those who do not have such experiences.

All examples of descriptive hypotheses.

It is important to note that the Descriptive hypothesis does not always have variables that can be designated as independent or dependent.

Relational Hypotheses

Relational hypotheses, on the other hand, are statements that describe the relationship between variables concerning some cases.

• Communities with many modern facilities will have a higher rate of contraception than communities with few modern facilities.

In this instance, the case is ‘communities,’ and the variables are ‘rate of contraception’ and ‘modern facilities.’

Similarly, “People who use chewing tobacco have a higher risk of oral carcinoma than people who have never used chewing tobacco” is a relational hypothesis.

A relational hypothesis is again of two types: correlational hypothesis and the causal hypothesis.

A correlational hypothesis states that variables occur in some predictable relationships without implying that one variable causes the other to change or take on different values.

Here is an example of a co-relational hypothesis:

• Males are more efficient than their female counterparts in typing.

In making such a statement, we do not claim that sex (male-female) as a variable influences the other variable,’ typing efficiency’ (less efficient-more efficient). Here is one more example of a correlational hypothesis:

• Saving habit is more pronounced among Christians than the people of other religions.

Once again, religion is not believed to be a factor in saving habits, although a positive relationship has been observed.

Look at the following example:

• The participation of women in household decision making increases with age, their level of education, and the number of surviving children.

Here too, women’s education, several surviving children, or education does not guarantee their decision-making autonomy.

With causal hypotheses (also called explanatory hypotheses), on the other hand, there is an implication that a change in one variable causes a change or leads to an effect on the other variable.

A causal variable is typically called an independent variable, and the other is the dependent variable. It is important to note that the term “cause” roughly means “help make happen.” So, the independent variable need not be the sole reason for the existence of or change in the dependent variable. Here are some examples of causal hypotheses:

• An increase in family income leads to an increase in the income saved.
• Exposure of mothers to mass media increases their knowledge of malnutrition among their children.
• An offer of a discount in a department store enhances the sales volume.
• Chewing tobacco increases the risk of oral carcinoma.
• Goat farming contributes to poverty alleviation of rural people.
• The utilization of child welfare clinics is the lowest in those clinics in which the clinic personnel are poorly motivated to provide preventive services.
• An increase in bank interest rate encourages the customers for increased savings.

In the above example, we have ample reasons to believe that one variable (family income and savings, misuse of credit, and farm size) has a bearing on the other variable.

We cite two more examples to illustrate the hypothesis, general objective, ultimate objective, and a few specific objectives.

General objective:

• To compare the complications of acceptors of laparoscopic sterilization and mini-laparotomy among American women.

Research hypothesis:

• The risk of complications is higher in the mini-laparotomy method of sterilization than in laparoscopic sterilization.

Specific objectives:

• To assess the complications of laparoscopic sterilization and mini-laparotomy.
• To assess service providers’ knowledge and perception regarding the complications, preferences, and convenience of the two methods.

Ultimate Objectives:

• To introduce and popularize the laparoscopic female sterilization method in the National Family Planning Program to reduce the rapid population growth rate.

In a study designed to examine the living and working conditions of the overseas migrant workers from India and the pattern of remittances from overseas migrant workers, the general objective, specific objectives, and the ultimate objective were formulated as follows:

• To examine the living and working conditions of the overseas migrant workers from India.”
• Characteristics of migrant workers by significant migration channels;
• Countries of destination;
• The occupational skill of the workers;
• Pattern and procedures of remittances;
• Impact of remittances on government revenue;
• Better utilization of remittances.

Ultimate objective:

• To suggest ways and means to minimize the differences in the policy adopted by the public and private sectors in their recruitment process in the interest of the workers;
• To ascertain the possible exploitation of the workers by the private agencies and suggest remedies for such exploitation.
• Private agencies, in most cases, exploit migrant workers.

What are the elements of a good hypothesis?

A good hypothesis should state the purpose of the research, identify which variables are to be used, be logical, precise in language, and be testable with research or experimentation.

How is a hypothesis typically structured?

A hypothesis often follows a basic format of “If {this happens}, then {this will happen}.” It proposes that if something is done, then a specific outcome will occur.

What is a Descriptive hypothesis?

Descriptive hypotheses are propositions that typically state some variables’ existence, size, form, or distribution. They are formulated in the form of statements in which variables are assigned to cases.

What distinguishes a Relational hypothesis?

Relational hypotheses describe the relationship between variables concerning some cases. They can be correlational, where variables occur in a predictable relationship without implying causation, or causal, where a change in one variable causes a change in another.

What is the difference between a correlational hypothesis and a causal hypothesis?

A correlational hypothesis states that variables occur in some predictable relationships without implying that one variable causes the other to change. A causal hypothesis, on the other hand, implies that a change in one variable causes a change or leads to an effect on the other variable.

What are the two main types of research hypotheses?

The two main types of research hypotheses are Descriptive hypothesis and Relational hypothesis

What is a hypothesis in the context of academic research?

A hypothesis is a statement about an expected relationship between variables or an explanation of an occurrence that is clear, specific, and testable.

How does a research hypothesis differ from a general hypothesis?

A research hypothesis is more specific and clear about what’s being assessed and the expected outcome. It must also be testable, meaning there should be a way to prove or disprove it.

What are the essential attributes of a good research hypothesis?

A good research hypothesis should have specificity, clarity, and testability.

Why is testability crucial for a research hypothesis?

Testability ensures that empirical research can prove or disproven the hypothesis. If a statement isn’t testable, it doesn’t qualify as a research hypothesis.

What is the null hypothesis?

The null hypothesis is the counter-proposal to the original hypothesis. It predicts that there is no relationship between the variables in question.

How can one ensure that a hypothesis is clear and specific?

A hypothesis should clearly identify the variables involved, the parties involved, and the expected relationship type, leaving no ambiguity about its intent or meaning.

Why is it essential to avoid value judgments in a research hypothesis?

Value judgments are subjective and not appropriate for a hypothesis. A research hypothesis should strive to be objective, avoiding personal opinions.

What is the basic definition of a hypothesis in research?

A research hypothesis is a statement about an expected relationship between variables, or an explanation of an occurrence, that is clear, specific, and testable.

While a general hypothesis is an idea or explanation based on known facts but not yet proven, a research hypothesis is a clear, specific, and testable statement about the expected outcome of a study.

What are the essential characteristics of a good research hypothesis?

A good research hypothesis should possess specificity, clarity, and testability. It should clearly define what’s being assessed and the expected outcome, and it must be possible to prove or disprove the statement through experimentation.

How can one ensure that a hypothesis is testable?

A hypothesis is testable if there’s a possibility to prove both its truth and falsity. The results of the hypothesis should be reproducible, and it should be specific enough to allow for clear testing procedures.

What is the difference between a null hypothesis and an alternative hypothesis?

The null hypothesis proposes that no statistical significance exists in a set of observations, suggesting any differences are due to chance alone. The alternative hypothesis, on the other hand, predicts a relationship between the variables of the study and states that the results are significant to the research topic.

How should one formulate an effective research hypothesis?

To formulate an effective research hypothesis, one should state the problem clearly, use an ‘if-then’ statement structure, define the variables as dependent or independent, and scrutinize the hypothesis to ensure it meets the criteria of specificity, clarity, and testability.

What are some types of hypotheses in research?

Types of hypotheses include simple, complex, directional, non-directional, associative and causal, empirical, and statistical hypotheses. Each type serves a specific purpose and is used based on the nature of the research question or problem.

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Definition of a Hypothesis

What it is and how it's used in sociology

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A hypothesis is a prediction of what will be found at the outcome of a research project and is typically focused on the relationship between two different variables studied in the research. It is usually based on both theoretical expectations about how things work and already existing scientific evidence.

Within social science, a hypothesis can take two forms. It can predict that there is no relationship between two variables, in which case it is a null hypothesis . Or, it can predict the existence of a relationship between variables, which is known as an alternative hypothesis.

In either case, the variable that is thought to either affect or not affect the outcome is known as the independent variable, and the variable that is thought to either be affected or not is the dependent variable.

Researchers seek to determine whether or not their hypothesis, or hypotheses if they have more than one, will prove true. Sometimes they do, and sometimes they do not. Either way, the research is considered successful if one can conclude whether or not a hypothesis is true. 

Null Hypothesis

A researcher has a null hypothesis when she or he believes, based on theory and existing scientific evidence, that there will not be a relationship between two variables. For example, when examining what factors influence a person's highest level of education within the U.S., a researcher might expect that place of birth, number of siblings, and religion would not have an impact on the level of education. This would mean the researcher has stated three null hypotheses.

Alternative Hypothesis

Taking the same example, a researcher might expect that the economic class and educational attainment of one's parents, and the race of the person in question are likely to have an effect on one's educational attainment. Existing evidence and social theories that recognize the connections between wealth and cultural resources , and how race affects access to rights and resources in the U.S. , would suggest that both economic class and educational attainment of the one's parents would have a positive effect on educational attainment. In this case, economic class and educational attainment of one's parents are independent variables, and one's educational attainment is the dependent variable—it is hypothesized to be dependent on the other two.

Conversely, an informed researcher would expect that being a race other than white in the U.S. is likely to have a negative impact on a person's educational attainment. This would be characterized as a negative relationship, wherein being a person of color has a negative effect on one's educational attainment. In reality, this hypothesis proves true, with the exception of Asian Americans , who go to college at a higher rate than whites do. However, Blacks and Hispanics and Latinos are far less likely than whites and Asian Americans to go to college.

Formulating a Hypothesis

Formulating a hypothesis can take place at the very beginning of a research project , or after a bit of research has already been done. Sometimes a researcher knows right from the start which variables she is interested in studying, and she may already have a hunch about their relationships. Other times, a researcher may have an interest in ​a particular topic, trend, or phenomenon, but he may not know enough about it to identify variables or formulate a hypothesis.

Whenever a hypothesis is formulated, the most important thing is to be precise about what one's variables are, what the nature of the relationship between them might be, and how one can go about conducting a study of them.

Updated by Nicki Lisa Cole, Ph.D

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How to Develop a Good Research Hypothesis

The story of a research study begins by asking a question. Researchers all around the globe are asking curious questions and formulating research hypothesis. However, whether the research study provides an effective conclusion depends on how well one develops a good research hypothesis. Research hypothesis examples could help researchers get an idea as to how to write a good research hypothesis.

This blog will help you understand what is a research hypothesis, its characteristics and, how to formulate a research hypothesis

Table of Contents

What is Hypothesis?

Hypothesis is an assumption or an idea proposed for the sake of argument so that it can be tested. It is a precise, testable statement of what the researchers predict will be outcome of the study.  Hypothesis usually involves proposing a relationship between two variables: the independent variable (what the researchers change) and the dependent variable (what the research measures).

What is a Research Hypothesis?

Research hypothesis is a statement that introduces a research question and proposes an expected result. It is an integral part of the scientific method that forms the basis of scientific experiments. Therefore, you need to be careful and thorough when building your research hypothesis. A minor flaw in the construction of your hypothesis could have an adverse effect on your experiment. In research, there is a convention that the hypothesis is written in two forms, the null hypothesis, and the alternative hypothesis (called the experimental hypothesis when the method of investigation is an experiment).

Characteristics of a Good Research Hypothesis

As the hypothesis is specific, there is a testable prediction about what you expect to happen in a study. You may consider drawing hypothesis from previously published research based on the theory.

A good research hypothesis involves more effort than just a guess. In particular, your hypothesis may begin with a question that could be further explored through background research.

To help you formulate a promising research hypothesis, you should ask yourself the following questions:

• Is the language clear and focused?
• What is the relationship between your hypothesis and your research topic?
• Is your hypothesis testable? If yes, then how?
• What are the possible explanations that you might want to explore?
• Does your hypothesis include both an independent and dependent variable?
• Can you manipulate your variables without hampering the ethical standards?
• Does your research predict the relationship and outcome?
• Is your research simple and concise (avoids wordiness)?
• Is it clear with no ambiguity or assumptions about the readers’ knowledge
• Is your research observable and testable results?
• Is it relevant and specific to the research question or problem?

The questions listed above can be used as a checklist to make sure your hypothesis is based on a solid foundation. Furthermore, it can help you identify weaknesses in your hypothesis and revise it if necessary.

Source: Educational Hub

How to formulate a research hypothesis.

A testable hypothesis is not a simple statement. It is rather an intricate statement that needs to offer a clear introduction to a scientific experiment, its intentions, and the possible outcomes. However, there are some important things to consider when building a compelling hypothesis.

1. State the problem that you are trying to solve.

Make sure that the hypothesis clearly defines the topic and the focus of the experiment.

2. Try to write the hypothesis as an if-then statement.

Follow this template: If a specific action is taken, then a certain outcome is expected.

3. Define the variables

Independent variables are the ones that are manipulated, controlled, or changed. Independent variables are isolated from other factors of the study.

Dependent variables , as the name suggests are dependent on other factors of the study. They are influenced by the change in independent variable.

4. Scrutinize the hypothesis

Evaluate assumptions, predictions, and evidence rigorously to refine your understanding.

Types of Research Hypothesis

The types of research hypothesis are stated below:

1. Simple Hypothesis

It predicts the relationship between a single dependent variable and a single independent variable.

2. Complex Hypothesis

It predicts the relationship between two or more independent and dependent variables.

3. Directional Hypothesis

It specifies the expected direction to be followed to determine the relationship between variables and is derived from theory. Furthermore, it implies the researcher’s intellectual commitment to a particular outcome.

4. Non-directional Hypothesis

It does not predict the exact direction or nature of the relationship between the two variables. The non-directional hypothesis is used when there is no theory involved or when findings contradict previous research.

5. Associative and Causal Hypothesis

The associative hypothesis defines interdependency between variables. A change in one variable results in the change of the other variable. On the other hand, the causal hypothesis proposes an effect on the dependent due to manipulation of the independent variable.

6. Null Hypothesis

Null hypothesis states a negative statement to support the researcher’s findings that there is no relationship between two variables. There will be no changes in the dependent variable due the manipulation of the independent variable. Furthermore, it states results are due to chance and are not significant in terms of supporting the idea being investigated.

7. Alternative Hypothesis

It states that there is a relationship between the two variables of the study and that the results are significant to the research topic. An experimental hypothesis predicts what changes will take place in the dependent variable when the independent variable is manipulated. Also, it states that the results are not due to chance and that they are significant in terms of supporting the theory being investigated.

Research Hypothesis Examples of Independent and Dependent Variables

Research Hypothesis Example 1 The greater number of coal plants in a region (independent variable) increases water pollution (dependent variable). If you change the independent variable (building more coal factories), it will change the dependent variable (amount of water pollution).

Research Hypothesis Example 2 What is the effect of diet or regular soda (independent variable) on blood sugar levels (dependent variable)? If you change the independent variable (the type of soda you consume), it will change the dependent variable (blood sugar levels)

You should not ignore the importance of the above steps. The validity of your experiment and its results rely on a robust testable hypothesis. Developing a strong testable hypothesis has few advantages, it compels us to think intensely and specifically about the outcomes of a study. Consequently, it enables us to understand the implication of the question and the different variables involved in the study. Furthermore, it helps us to make precise predictions based on prior research. Hence, forming a hypothesis would be of great value to the research. Here are some good examples of testable hypotheses.

More importantly, you need to build a robust testable research hypothesis for your scientific experiments. A testable hypothesis is a hypothesis that can be proved or disproved as a result of experimentation.

Importance of a Testable Hypothesis

To devise and perform an experiment using scientific method, you need to make sure that your hypothesis is testable. To be considered testable, some essential criteria must be met:

• There must be a possibility to prove that the hypothesis is true.
• There must be a possibility to prove that the hypothesis is false.
• The results of the hypothesis must be reproducible.

Without these criteria, the hypothesis and the results will be vague. As a result, the experiment will not prove or disprove anything significant.

What are your experiences with building hypotheses for scientific experiments? What challenges did you face? How did you overcome these challenges? Please share your thoughts with us in the comments section.

Frequently Asked Questions

The steps to write a research hypothesis are: 1. Stating the problem: Ensure that the hypothesis defines the research problem 2. Writing a hypothesis as an 'if-then' statement: Include the action and the expected outcome of your study by following a ‘if-then’ structure. 3. Defining the variables: Define the variables as Dependent or Independent based on their dependency to other factors. 4. Scrutinizing the hypothesis: Identify the type of your hypothesis

Hypothesis testing is a statistical tool which is used to make inferences about a population data to draw conclusions for a particular hypothesis.

Hypothesis in statistics is a formal statement about the nature of a population within a structured framework of a statistical model. It is used to test an existing hypothesis by studying a population.

Research hypothesis is a statement that introduces a research question and proposes an expected result. It forms the basis of scientific experiments.

The different types of hypothesis in research are: • Null hypothesis: Null hypothesis is a negative statement to support the researcher’s findings that there is no relationship between two variables. • Alternate hypothesis: Alternate hypothesis predicts the relationship between the two variables of the study. • Directional hypothesis: Directional hypothesis specifies the expected direction to be followed to determine the relationship between variables. • Non-directional hypothesis: Non-directional hypothesis does not predict the exact direction or nature of the relationship between the two variables. • Simple hypothesis: Simple hypothesis predicts the relationship between a single dependent variable and a single independent variable. • Complex hypothesis: Complex hypothesis predicts the relationship between two or more independent and dependent variables. • Associative and casual hypothesis: Associative and casual hypothesis predicts the relationship between two or more independent and dependent variables. • Empirical hypothesis: Empirical hypothesis can be tested via experiments and observation. • Statistical hypothesis: A statistical hypothesis utilizes statistical models to draw conclusions about broader populations.

Wow! You really simplified your explanation that even dummies would find it easy to comprehend. Thank you so much.

Thanks a lot for your valuable guidance.

I enjoy reading the post. Hypotheses are actually an intrinsic part in a study. It bridges the research question and the methodology of the study.

Useful piece!

This is awesome.Wow.

It very interesting to read the topic, can you guide me any specific example of hypothesis process establish throw the Demand and supply of the specific product in market

Nicely explained

It is really a useful for me Kindly give some examples of hypothesis

It was a well explained content ,can you please give me an example with the null and alternative hypothesis illustrated

clear and concise. thanks.

So Good so Amazing

Good to learn

Thanks a lot for explaining to my level of understanding

Explained well and in simple terms. Quick read! Thank you

It awesome. It has really positioned me in my research project

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Definition of hypothesis

Did you know.

The Difference Between Hypothesis and Theory

A hypothesis is an assumption, an idea that is proposed for the sake of argument so that it can be tested to see if it might be true.

In the scientific method, the hypothesis is constructed before any applicable research has been done, apart from a basic background review. You ask a question, read up on what has been studied before, and then form a hypothesis.

A hypothesis is usually tentative; it's an assumption or suggestion made strictly for the objective of being tested.

A theory , in contrast, is a principle that has been formed as an attempt to explain things that have already been substantiated by data. It is used in the names of a number of principles accepted in the scientific community, such as the Big Bang Theory . Because of the rigors of experimentation and control, it is understood to be more likely to be true than a hypothesis is.

In non-scientific use, however, hypothesis and theory are often used interchangeably to mean simply an idea, speculation, or hunch, with theory being the more common choice.

Since this casual use does away with the distinctions upheld by the scientific community, hypothesis and theory are prone to being wrongly interpreted even when they are encountered in scientific contexts—or at least, contexts that allude to scientific study without making the critical distinction that scientists employ when weighing hypotheses and theories.

The most common occurrence is when theory is interpreted—and sometimes even gleefully seized upon—to mean something having less truth value than other scientific principles. (The word law applies to principles so firmly established that they are almost never questioned, such as the law of gravity.)

This mistake is one of projection: since we use theory in general to mean something lightly speculated, then it's implied that scientists must be talking about the same level of uncertainty when they use theory to refer to their well-tested and reasoned principles.

The distinction has come to the forefront particularly on occasions when the content of science curricula in schools has been challenged—notably, when a school board in Georgia put stickers on textbooks stating that evolution was "a theory, not a fact, regarding the origin of living things." As Kenneth R. Miller, a cell biologist at Brown University, has said , a theory "doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.”

While theories are never completely infallible, they form the basis of scientific reasoning because, as Miller said "to the best of our ability, we’ve tested them, and they’ve held up."

• proposition
• supposition

hypothesis , theory , law mean a formula derived by inference from scientific data that explains a principle operating in nature.

hypothesis implies insufficient evidence to provide more than a tentative explanation.

theory implies a greater range of evidence and greater likelihood of truth.

law implies a statement of order and relation in nature that has been found to be invariable under the same conditions.

Examples of hypothesis in a Sentence

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'hypothesis.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

Greek, from hypotithenai to put under, suppose, from hypo- + tithenai to put — more at do

1641, in the meaning defined at sense 1a

Phrases Containing hypothesis

• counter - hypothesis
• nebular hypothesis
• null hypothesis
• planetesimal hypothesis
• Whorfian hypothesis

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This is the Difference Between a...

This is the Difference Between a Hypothesis and a Theory

In scientific reasoning, they're two completely different things

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Cite this Entry

“Hypothesis.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/hypothesis. Accessed 19 Apr. 2024.

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7.3: The Research Hypothesis and the Null Hypothesis

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• Page ID 18038

• Michelle Oja
• Taft College

Hypotheses are predictions of expected findings.

The Research Hypothesis

A research hypothesis is a mathematical way of stating a research question.  A research hypothesis names the groups (we'll start with a sample and a population), what was measured, and which we think will have a higher mean.  The last one gives the research hypothesis a direction.  In other words, a research hypothesis should include:

• The name of the groups being compared.  This is sometimes considered the IV.
• What was measured.  This is the DV.
• Which group are we predicting will have the higher mean.  

There are two types of research hypotheses related to sample means and population means:  Directional Research Hypotheses and Non-Directional Research Hypotheses

Directional Research Hypothesis

If we expect our obtained sample mean to be above or below the other group's mean (the population mean, for example), we have a directional hypothesis. There are two options:

• Symbol:       \( \displaystyle \bar{X} > \mu \)
• (The mean of the sample is greater than than the mean of the population.)
• Symbol:     \( \displaystyle \bar{X} < \mu \)
• (The mean of the sample is less than than mean of the population.)

Example \(\PageIndex{1}\)

A study by Blackwell, Trzesniewski, and Dweck (2007) measured growth mindset and how long the junior high student participants spent on their math homework.  What’s a directional hypothesis for how scoring higher on growth mindset (compared to the population of junior high students) would be related to how long students spent on their homework?  Write this out in words and symbols.

Answer in Words:            Students who scored high on growth mindset would spend more time on their homework than the population of junior high students.

Answer in Symbols:         \( \displaystyle \bar{X} > \mu \) 

Non-Directional Research Hypothesis

A non-directional hypothesis states that the means will be different, but does not specify which will be higher.  In reality, there is rarely a situation in which we actually don't want one group to be higher than the other, so we will focus on directional research hypotheses.  There is only one option for a non-directional research hypothesis: "The sample mean differs from the population mean."  These types of research hypotheses don’t give a direction, the hypothesis doesn’t say which will be higher or lower.

A non-directional research hypothesis in symbols should look like this:    \( \displaystyle \bar{X} \neq \mu \) (The mean of the sample is not equal to the mean of the population).

Exercise \(\PageIndex{1}\)

What’s a non-directional hypothesis for how scoring higher on growth mindset higher on growth mindset (compared to the population of junior high students) would be related to how long students spent on their homework (Blackwell, Trzesniewski, & Dweck, 2007)?  Write this out in words and symbols.

Answer in Words:            Students who scored high on growth mindset would spend a different amount of time on their homework than the population of junior high students.

Answer in Symbols:        \( \displaystyle \bar{X} \neq \mu \) 

See how a non-directional research hypothesis doesn't really make sense?  The big issue is not if the two groups differ, but if one group seems to improve what was measured (if having a growth mindset leads to more time spent on math homework).  This textbook will only use directional research hypotheses because researchers almost always have a predicted direction (meaning that we almost always know which group we think will score higher).

The Null Hypothesis

The hypothesis that an apparent effect is due to chance is called the null hypothesis, written \(H_0\) (“H-naught”). We usually test this through comparing an experimental group to a comparison (control) group.  This null hypothesis can be written as:

\[\mathrm{H}_{0}: \bar{X} = \mu \nonumber \]

For most of this textbook, the null hypothesis is that the means of the two groups are similar.  Much later, the null hypothesis will be that there is no relationship between the two groups.  Either way, remember that a null hypothesis is always saying that nothing is different.  

This is where descriptive statistics diverge from inferential statistics.  We know what the value of \(\overline{\mathrm{X}}\) is – it’s not a mystery or a question, it is what we observed from the sample.  What we are using inferential statistics to do is infer whether this sample's descriptive statistics probably represents the population's descriptive statistics.  This is the null hypothesis, that the two groups are similar.  

Keep in mind that the null hypothesis is typically the opposite of the research hypothesis. A research hypothesis for the ESP example is that those in my sample who say that they have ESP would get more correct answers than the population would get correct, while the null hypothesis is that the average number correct for the two groups will be similar. 

In general, the null hypothesis is the idea that nothing is going on: there is no effect of our treatment, no relation between our variables, and no difference in our sample mean from what we expected about the population mean. This is always our baseline starting assumption, and it is what we seek to reject. If we are trying to treat depression, we want to find a difference in average symptoms between our treatment and control groups. If we are trying to predict job performance, we want to find a relation between conscientiousness and evaluation scores. However, until we have evidence against it, we must use the null hypothesis as our starting point.

In sum, the null hypothesis is always : There is no difference between the groups’ means OR There is no relationship between the variables .

In the next chapter, the null hypothesis is that there’s no difference between the sample mean   and population mean.  In other words:

• There is no mean difference between the sample and population.
• The mean of the sample is the same as the mean of a specific population.
• \(\mathrm{H}_{0}: \bar{X} = \mu \nonumber \)
• We expect our sample’s mean to be same as the population mean.

Exercise \(\PageIndex{2}\)

A study by Blackwell, Trzesniewski, and Dweck (2007) measured growth mindset and how long the junior high student participants spent on their math homework.  What’s the null hypothesis for scoring higher on growth mindset (compared to the population of junior high students) and how long students spent on their homework?  Write this out in words and symbols.

Answer in Words:            Students who scored high on growth mindset would spend a similar amount of time on their homework as the population of junior high students.

Answer in Symbols:    \( \bar{X} = \mu \)

Contributors and Attributions

Foster et al.  (University of Missouri-St. Louis, Rice University, & University of Houston, Downtown Campus)

Dr. MO ( Taft College )

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• v.53(4); 2010 Aug

Research questions, hypotheses and objectives

Patricia farrugia.

* Michael G. DeGroote School of Medicine, the

Bradley A. Petrisor

† Division of Orthopaedic Surgery and the

Forough Farrokhyar

‡ Departments of Surgery and

§ Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ont

Mohit Bhandari

There is an increasing familiarity with the principles of evidence-based medicine in the surgical community. As surgeons become more aware of the hierarchy of evidence, grades of recommendations and the principles of critical appraisal, they develop an increasing familiarity with research design. Surgeons and clinicians are looking more and more to the literature and clinical trials to guide their practice; as such, it is becoming a responsibility of the clinical research community to attempt to answer questions that are not only well thought out but also clinically relevant. The development of the research question, including a supportive hypothesis and objectives, is a necessary key step in producing clinically relevant results to be used in evidence-based practice. A well-defined and specific research question is more likely to help guide us in making decisions about study design and population and subsequently what data will be collected and analyzed. 1

Objectives of this article

In this article, we discuss important considerations in the development of a research question and hypothesis and in defining objectives for research. By the end of this article, the reader will be able to appreciate the significance of constructing a good research question and developing hypotheses and research objectives for the successful design of a research study. The following article is divided into 3 sections: research question, research hypothesis and research objectives.

Research question

Interest in a particular topic usually begins the research process, but it is the familiarity with the subject that helps define an appropriate research question for a study. 1 Questions then arise out of a perceived knowledge deficit within a subject area or field of study. 2 Indeed, Haynes suggests that it is important to know “where the boundary between current knowledge and ignorance lies.” 1 The challenge in developing an appropriate research question is in determining which clinical uncertainties could or should be studied and also rationalizing the need for their investigation.

Increasing one’s knowledge about the subject of interest can be accomplished in many ways. Appropriate methods include systematically searching the literature, in-depth interviews and focus groups with patients (and proxies) and interviews with experts in the field. In addition, awareness of current trends and technological advances can assist with the development of research questions. 2 It is imperative to understand what has been studied about a topic to date in order to further the knowledge that has been previously gathered on a topic. Indeed, some granting institutions (e.g., Canadian Institute for Health Research) encourage applicants to conduct a systematic review of the available evidence if a recent review does not already exist and preferably a pilot or feasibility study before applying for a grant for a full trial.

In-depth knowledge about a subject may generate a number of questions. It then becomes necessary to ask whether these questions can be answered through one study or if more than one study needed. 1 Additional research questions can be developed, but several basic principles should be taken into consideration. 1 All questions, primary and secondary, should be developed at the beginning and planning stages of a study. Any additional questions should never compromise the primary question because it is the primary research question that forms the basis of the hypothesis and study objectives. It must be kept in mind that within the scope of one study, the presence of a number of research questions will affect and potentially increase the complexity of both the study design and subsequent statistical analyses, not to mention the actual feasibility of answering every question. 1 A sensible strategy is to establish a single primary research question around which to focus the study plan. 3 In a study, the primary research question should be clearly stated at the end of the introduction of the grant proposal, and it usually specifies the population to be studied, the intervention to be implemented and other circumstantial factors. 4

Hulley and colleagues 2 have suggested the use of the FINER criteria in the development of a good research question ( Box 1 ). The FINER criteria highlight useful points that may increase the chances of developing a successful research project. A good research question should specify the population of interest, be of interest to the scientific community and potentially to the public, have clinical relevance and further current knowledge in the field (and of course be compliant with the standards of ethical boards and national research standards).

FINER criteria for a good research question

Adapted with permission from Wolters Kluwer Health. 2

Whereas the FINER criteria outline the important aspects of the question in general, a useful format to use in the development of a specific research question is the PICO format — consider the population (P) of interest, the intervention (I) being studied, the comparison (C) group (or to what is the intervention being compared) and the outcome of interest (O). 3 , 5 , 6 Often timing (T) is added to PICO ( Box 2 ) — that is, “Over what time frame will the study take place?” 1 The PICOT approach helps generate a question that aids in constructing the framework of the study and subsequently in protocol development by alluding to the inclusion and exclusion criteria and identifying the groups of patients to be included. Knowing the specific population of interest, intervention (and comparator) and outcome of interest may also help the researcher identify an appropriate outcome measurement tool. 7 The more defined the population of interest, and thus the more stringent the inclusion and exclusion criteria, the greater the effect on the interpretation and subsequent applicability and generalizability of the research findings. 1 , 2 A restricted study population (and exclusion criteria) may limit bias and increase the internal validity of the study; however, this approach will limit external validity of the study and, thus, the generalizability of the findings to the practical clinical setting. Conversely, a broadly defined study population and inclusion criteria may be representative of practical clinical practice but may increase bias and reduce the internal validity of the study.

PICOT criteria 1

A poorly devised research question may affect the choice of study design, potentially lead to futile situations and, thus, hamper the chance of determining anything of clinical significance, which will then affect the potential for publication. Without devoting appropriate resources to developing the research question, the quality of the study and subsequent results may be compromised. During the initial stages of any research study, it is therefore imperative to formulate a research question that is both clinically relevant and answerable.

Research hypothesis

The primary research question should be driven by the hypothesis rather than the data. 1 , 2 That is, the research question and hypothesis should be developed before the start of the study. This sounds intuitive; however, if we take, for example, a database of information, it is potentially possible to perform multiple statistical comparisons of groups within the database to find a statistically significant association. This could then lead one to work backward from the data and develop the “question.” This is counterintuitive to the process because the question is asked specifically to then find the answer, thus collecting data along the way (i.e., in a prospective manner). Multiple statistical testing of associations from data previously collected could potentially lead to spuriously positive findings of association through chance alone. 2 Therefore, a good hypothesis must be based on a good research question at the start of a trial and, indeed, drive data collection for the study.

The research or clinical hypothesis is developed from the research question and then the main elements of the study — sampling strategy, intervention (if applicable), comparison and outcome variables — are summarized in a form that establishes the basis for testing, statistical and ultimately clinical significance. 3 For example, in a research study comparing computer-assisted acetabular component insertion versus freehand acetabular component placement in patients in need of total hip arthroplasty, the experimental group would be computer-assisted insertion and the control/conventional group would be free-hand placement. The investigative team would first state a research hypothesis. This could be expressed as a single outcome (e.g., computer-assisted acetabular component placement leads to improved functional outcome) or potentially as a complex/composite outcome; that is, more than one outcome (e.g., computer-assisted acetabular component placement leads to both improved radiographic cup placement and improved functional outcome).

However, when formally testing statistical significance, the hypothesis should be stated as a “null” hypothesis. 2 The purpose of hypothesis testing is to make an inference about the population of interest on the basis of a random sample taken from that population. The null hypothesis for the preceding research hypothesis then would be that there is no difference in mean functional outcome between the computer-assisted insertion and free-hand placement techniques. After forming the null hypothesis, the researchers would form an alternate hypothesis stating the nature of the difference, if it should appear. The alternate hypothesis would be that there is a difference in mean functional outcome between these techniques. At the end of the study, the null hypothesis is then tested statistically. If the findings of the study are not statistically significant (i.e., there is no difference in functional outcome between the groups in a statistical sense), we cannot reject the null hypothesis, whereas if the findings were significant, we can reject the null hypothesis and accept the alternate hypothesis (i.e., there is a difference in mean functional outcome between the study groups), errors in testing notwithstanding. In other words, hypothesis testing confirms or refutes the statement that the observed findings did not occur by chance alone but rather occurred because there was a true difference in outcomes between these surgical procedures. The concept of statistical hypothesis testing is complex, and the details are beyond the scope of this article.

Another important concept inherent in hypothesis testing is whether the hypotheses will be 1-sided or 2-sided. A 2-sided hypothesis states that there is a difference between the experimental group and the control group, but it does not specify in advance the expected direction of the difference. For example, we asked whether there is there an improvement in outcomes with computer-assisted surgery or whether the outcomes worse with computer-assisted surgery. We presented a 2-sided test in the above example because we did not specify the direction of the difference. A 1-sided hypothesis states a specific direction (e.g., there is an improvement in outcomes with computer-assisted surgery). A 2-sided hypothesis should be used unless there is a good justification for using a 1-sided hypothesis. As Bland and Atlman 8 stated, “One-sided hypothesis testing should never be used as a device to make a conventionally nonsignificant difference significant.”

The research hypothesis should be stated at the beginning of the study to guide the objectives for research. Whereas the investigators may state the hypothesis as being 1-sided (there is an improvement with treatment), the study and investigators must adhere to the concept of clinical equipoise. According to this principle, a clinical (or surgical) trial is ethical only if the expert community is uncertain about the relative therapeutic merits of the experimental and control groups being evaluated. 9 It means there must exist an honest and professional disagreement among expert clinicians about the preferred treatment. 9

Designing a research hypothesis is supported by a good research question and will influence the type of research design for the study. Acting on the principles of appropriate hypothesis development, the study can then confidently proceed to the development of the research objective.

Research objective

The primary objective should be coupled with the hypothesis of the study. Study objectives define the specific aims of the study and should be clearly stated in the introduction of the research protocol. 7 From our previous example and using the investigative hypothesis that there is a difference in functional outcomes between computer-assisted acetabular component placement and free-hand placement, the primary objective can be stated as follows: this study will compare the functional outcomes of computer-assisted acetabular component insertion versus free-hand placement in patients undergoing total hip arthroplasty. Note that the study objective is an active statement about how the study is going to answer the specific research question. Objectives can (and often do) state exactly which outcome measures are going to be used within their statements. They are important because they not only help guide the development of the protocol and design of study but also play a role in sample size calculations and determining the power of the study. 7 These concepts will be discussed in other articles in this series.

From the surgeon’s point of view, it is important for the study objectives to be focused on outcomes that are important to patients and clinically relevant. For example, the most methodologically sound randomized controlled trial comparing 2 techniques of distal radial fixation would have little or no clinical impact if the primary objective was to determine the effect of treatment A as compared to treatment B on intraoperative fluoroscopy time. However, if the objective was to determine the effect of treatment A as compared to treatment B on patient functional outcome at 1 year, this would have a much more significant impact on clinical decision-making. Second, more meaningful surgeon–patient discussions could ensue, incorporating patient values and preferences with the results from this study. 6 , 7 It is the precise objective and what the investigator is trying to measure that is of clinical relevance in the practical setting.

The following is an example from the literature about the relation between the research question, hypothesis and study objectives:

Study: Warden SJ, Metcalf BR, Kiss ZS, et al. Low-intensity pulsed ultrasound for chronic patellar tendinopathy: a randomized, double-blind, placebo-controlled trial. Rheumatology 2008;47:467–71.

Research question: How does low-intensity pulsed ultrasound (LIPUS) compare with a placebo device in managing the symptoms of skeletally mature patients with patellar tendinopathy?

Research hypothesis: Pain levels are reduced in patients who receive daily active-LIPUS (treatment) for 12 weeks compared with individuals who receive inactive-LIPUS (placebo).

Objective: To investigate the clinical efficacy of LIPUS in the management of patellar tendinopathy symptoms.

The development of the research question is the most important aspect of a research project. A research project can fail if the objectives and hypothesis are poorly focused and underdeveloped. Useful tips for surgical researchers are provided in Box 3 . Designing and developing an appropriate and relevant research question, hypothesis and objectives can be a difficult task. The critical appraisal of the research question used in a study is vital to the application of the findings to clinical practice. Focusing resources, time and dedication to these 3 very important tasks will help to guide a successful research project, influence interpretation of the results and affect future publication efforts.

Tips for developing research questions, hypotheses and objectives for research studies

• Perform a systematic literature review (if one has not been done) to increase knowledge and familiarity with the topic and to assist with research development.
• Learn about current trends and technological advances on the topic.
• Seek careful input from experts, mentors, colleagues and collaborators to refine your research question as this will aid in developing the research question and guide the research study.
• Use the FINER criteria in the development of the research question.
• Ensure that the research question follows PICOT format.
• Develop a research hypothesis from the research question.
• Develop clear and well-defined primary and secondary (if needed) objectives.
• Ensure that the research question and objectives are answerable, feasible and clinically relevant.

FINER = feasible, interesting, novel, ethical, relevant; PICOT = population (patients), intervention (for intervention studies only), comparison group, outcome of interest, time.

Competing interests: No funding was received in preparation of this paper. Dr. Bhandari was funded, in part, by a Canada Research Chair, McMaster University.

Define Hypothesis: Unveiling the First Step in Scientific Inquiry

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Welcome to the world of research, where you’ll journey through a universe brimming with questions and curiosity. In this cosmos, a hypothesis is one celestial object you can’t miss! Today’s expedition invites you on board an exploration to ‘Define Hypothesis.’ Hop in; it wouldn’t be hyperbole to state we’re about to unlock the nucleus behind every ever scientific theory and inquiry!

Definition of Hypothesis

Introduction to the concept of hypothesis.

Picture yourself as a detective solving a case. Right from inspecting clues, formulating potential theories on whodunit, putting these theories under rigorous tests until finally reaching that elusive conclusive evidence – exciting, isn’t it?

Now replace detective with researcher and voila – here comes our heavyweight term: Hypothesis. Much like how any plausible theory drives detectives’ investigations, scientific hypotheses are vital navigational compasses guiding researchers in their quest for scientific evolutions.

Explanation of What a Hypothesis Is in The Context of Research and Scientific Inquiry

A hypothesis – popularly known as an educated guess or predictive statement – represents an initial supposition or proposed explanation made on limited information but founded on validation-grounded knowledge. It forms the basis for preliminary exploration into a specific set of circumstances or natural phenomena beyond.

Formulated prior to conducting research, scientists employ hypotheses as testable conjectures to explain an observed behavior or event. Confused? Fret not. To put it simply and by example: “If I increase the frequency of watering my plants twice daily (instead of solely relying upon weather conditions), then they will grow faster.” Now that’s what we call an everyday-life hypothesis!

Remember, hypotheses are not wild guesses plucked out of thin air but rather preconceived assertions open to empirical verification. They mark the inception point for any scientific investigation and serve as cornerstones for further experiments.

Characteristics and Components of a Hypothesis

Key characteristics of a hypothesis.

Before plunging into the deep end to define a hypothesis, let’s brush up on the features that contribute to effective hypotheses. For starters, a strong hypothesis is testable. This means it must be possible for empirical evidence to either support the word hypothesis or contradict it. The proposal should also be logically consistent and grounded firmly in existing knowledge.

Further down the line, another salient feature is specificity. Good hypotheses are not broad statements but instead focus on a specific aspect or phenomenon within the intended research field. Moreover, they are typically succinct and easily understandable ensuring information isn’t lost in translation among researchers.

Moreover, any well-structured hypothesis connects the independent and dependent variables together – typically, there’s at least one independent and one dependent variable involved. These elements form a relationship where changes instigated in the independent variable affect the values observed for the dependent variable.

Lastly but importantly, a solid hypothesis often carries potential implications for future research areas and can potentially lead to further tests and studies if verified.

Elements that make up a well-formulated hypothesis

Delving deeper into what shapes up a robust hypothesis, we realize that certain crucial components determine its effectiveness.

Firstly, every good hypothesis or test has clear variables which essentially refer to specific aspects of the study subject matter being measured or manipulated during research. These aspects are segregated as:

• Independent Variable (IV): This component relates directly to what you have control over in your study.
• Dependent Variable (DV): This component consists of outcomes affected by alterations made in IV

Next comes ‘Predicted Outcome’ – what you anticipate happening as repercussions due to modification of two or more variables under scrutiny.

The ‘Testability’ factor also holds veritable importance comprising experimental procedures capable enough to refute or accept your claims.

The last element circles the argument around presenting a capacity called ‘Relationship’ correlating IV with DV believed to either causing some effect or showcasing an association.

Hence, these prime facets further accentuate your endeavor to adequately define the hypothesis.

Importance and Purpose of a Hypothesis

Understanding the Role of a Hypothesis in Research

First, let’s delve into the overarching role that hypothesis plays within research scenarios. As we define the hypothesis, you should view this as an underlying pillar or guiding star for your investigation. A well-articulated hypothesis steers your exploration by providing clarity on what specifically you aim to examine.

A meaningful analogy would be considering a hypothesis as a compass during a voyage. If research is the vast ocean where confusing whirlpools of data and evidence abound, then it can guide us in our direction rather than letting us drift aimlessly. Furthermore, the formulation of a quality hypothesis inherently demands clarity about your objectives upfront – this essentially sets your research vessel on course bearing towards effective outcomes.

Exploring Why Formulating A Hypothesis is Crucial in Scientific Investigations

So why precisely is nurturing such a detailed forecast vital?

• Structural Advantage: By proposing potential answers to posed questions via hypotheses, researchers streamline their methods and techniques. The approach undertaken depends significantly on what the suggested outcome or phenomenon might be.
• Generate Preliminary Expectations: Even if they’re proven wrong, making observations and developing models based on hypotheses often lead to more interesting inquiries or turn up unexpected findings.
• Quantifiable Predictions: More than simple conjectures, strong hypotheses are testable; they propose results expressed in measurable terms.

In essence, remember that formulating hypotheses smoothes the path towards solid conclusions by being the architect’s blueprints of robust investigations. Never underestimate the forward thrust they provide for progress within scientific inquiry!

Types of Hypotheses

Once we understand to define a hypothesis, we’ll find that hypotheses come in several types. Different classifications of plural hypotheses depend on their formulations and the nature of predictions or assumptions they lead towards – simple, complex, directional, non-directional, null, associative and causal. Let’s explore some of these.

Simple Hypothesis: Definition and Examples

A simple hypothesis is a type of prediction or an educated guess that carries one independent variable and one dependent variable. In essence, it creates a relationship between two singular entities; for instance, ‘Exercise improves memory.’ This suggests that there’s an impact (of improvement) on the ‘memory’ (dependent variable) by ‘exercise’ (independent variable).

Complex Hypothesis: Definition and Examples

On the contrary to its name mate – a simple hypothesis – a complex hypothesis involves more than just two variables. It points out multiple variables and how they interlink with each other. The effects aren’t just limited to cause-and-effect but can be interactive or combined impact-dependent variables too – for instance,’Diet and exercise affect weight loss and heart health.’ Here, diet and exercise are your independent factors influencing multifold aspects like weight loss (a dependent variable) alongside heart health(another dependent variable).

Directional Hypothesis: Definition and Examples

One might argue that the path laid by a directional hypothesis is less twisted as it predicts the directionality of an effect – whether one variable will increase or decrease another variable. An example here could be “Cutting down on alcohol will reduce liver disorders.” Here a reduction in ‘drinking alcohol’ implicitly identifies fewer occurrences of ‘liver disorders.’

Non-directional Hypothesis: Definition and Examples

Sometimes science requires open-ended answers; henceforth comes into play our non-directional hypothesis which merely stipulates that there’s going to be an impact without specifying its course – good, bad or otherwise. For example, “Exposure to secondhand smoke influences lung health.” It infers that there’s an effect on ‘lung health’ due to ‘secondhand smoke,’ without indicating if it’s an improvement or deterioration.

Null Hypothesis: Definition and Examples

The null hypothesis, often symbolized as H0, makes things pretty straight with assumptions; basically, it purports no existence of a relationship between the variables. Researchers utilize this hypothesis chiefly for statistical testing. In lay terms – “Smoking is not linked to lung cancer.” Here a nonexistence of association is suggested between ‘smoking’ and ‘lung cancer.’

Associative and Causal Hypothesis: Explanation and Examples

Now leaving the train station named Null-ville we enter into quite associative terrain where the associative hypothesis foretells ‘relationships’ but are shy when it comes to cause-effects. An instance could be “Students scoring high also tend to play chess.” These fellows here don’t claim that playing chess outrightly shoots up scores yet suggests a specific pattern.

On another spectrum brightful cause-effect claims jump in bravely shouting out not just relationships but boldly stating their causes too – “Consumption of fast food leads to obesity” is being so certain about fast food consumption (cause) escalating obesity levels(effect).

Navigating through these alternative hypotheses and variants allows us to step into researchers’ shoes better while also helps defining complex constructions bit by bit, making them simple outcomes anyone can interpret.

Developing and Testing a Hypothesis

In the world of research, it’s not uncommon to hear someone say “Let’s define hypothesis!” This term may seem complex at first glance, but its essence falls within our natural instinct to question and learn. To give structure to this innate curiosity, we form hypotheses and navigate through the rigorous process of testing them.

Process of Formulating a Hypothesis

Forming an effective hypothesis is both an art and a science. It involves finding a perfect blend between creativity and logical reasoning. Here are some simple yet essential steps you’d want to follow:

• Identify Your Research Question – The first step towards formulating a hypothesis is defining your research question based on preliminary observations or literature review.
• Conduct Thorough Literature Review – Once your question is in place, an extensive read about what has already been studied can help refine it further.
• Create Tentative Explanation – Develop a preliminary answer based on your knowledge and understanding which will serve as your tentative explanation or hypothesis.
• Refine Your Hypothesis : Refine this initial guess considering available resources for empirical testing, ethical implications, and potential outcomes.

Remember that the key is formation clarity in statement-making; overly complex language might obscure rather than clarify your central idea.

Importance of Testing a Hypothesis Through Empirical Research Methods

Testing a hypothesis isn’t simply about proving it right or wrong; it’s much more refined than that – it’s about validation and advancement of human knowledge. By applying empirical methods such as observation or experimentation, logic meets practice in real-world scenarios.

These hands-on approaches afford us precious insights into how our theories hold up under scrutiny outside the confines of abstract thought alone.

• Validity Confirmation : Empirical testing helps confirm if our predictions were correct or not, providing validation for our presumptions.
• Understanding Relationships : Testing allows us to assess the relational dynamics between variables under investigation.
• Promotes Scientific Inquiry : Empirical testing encourages a systematic and objective approach to understanding phenomena, which lies at the heart of scientific inquiry.

Consider this: hypotheses are our best-educated guesses – smart hunches rooted in what we know so far. To move beyond guessing and into knowledgeable assertion, we define hypothesis structure as one that can be empirically tested. Only then do we truly start to shape our understanding with any level of certainty.

Examples of Hypotheses in Different Fields

Indeed, it’s fundamental to understand that hypotheses are not confined to a single discipline but span across numerous fields. To better illuminate this, let’s delve into various examples.

Examples of Hypotheses in Scientific Research Studies

In the realm of scientific research studies, hypotheses play a pivotal role in shaping the basis for investigations research hypotheses and experiments. Let’s consider an elementary example: studying plant growth. A researcher might formulate the hypothesis – “If a specific type of fertilizer is used, then plants will grow more rapidly.” This hypothesis aims to validate or refute the assumption that given fertilizer perceptibly affects plant growth rate.

Another common example arises from investigating causal relationships between physical activity and heart health. The scientist may hypothesize that “Regular aerobic exercise decreases the risk of heart disease.”

Examples of Hypotheses in Social Sciences

When we transition towards social sciences, which deals with human behavior and its relation to societal constructs, our formative definitions undergo a change as well.

Imagine researchers examining how socioeconomic status influences educational attainment rates. They could pose a hypothesis saying, “High socioeconomic status positively correlates with higher levels of formal education.” This hypothesis attempts to tie economic background directly to education outcomes.

The correlation between gender diversity within workplace teams and improved business performance presents another illustration. A possible hypothesis could be – “Teams comprising diverse genders exhibit superior business performance than homogenous teams.”

Examples of Hypotheses in Psychology

Within psychology – the study dedicated to how individuals think, feel, and behave; clearly stated hypotheses serve as essential stepping stones for meaningful findings and insights.

Take, for instance, predicting performance under pressure: psychologists may propose an assumption like – “Stress triggers increased errors on complex tasks”. Or when researching cognitive development in children – they may hypothesize – “Language acquisition accelerates once children start attending school”.

Examples of Hypotheses in Medical Research

Lastly but importantly, in medical research, well-articulated hypotheses help probe pressing healthcare questions and identify effective treatments.

For instance: “Patients receiving chemotherapy experience significant weight loss”. Or regarding disease transmission during pandemics – they might propose “Regular hand sanitation reduces the risk of COVID-19 infection.”

In conclusion, these examples hopefully underline the importance and versatility of a hypothesis in scientific inquiry. Irrespective of its utilization within various research fields, a scientific hypothesis still essentially remains an educated assumption that offers direction and purpose to the investigation. Interestingly enough, each study’s defined hypothesis sets forth a path leading towards a better comprehension of our world and life within it.

Common Mistakes to Avoid when Formulating a Hypothesis

Identifying errors that researchers often make when developing a hypothesis.

Many researchers, especially those new in the field, may sometimes falter while crafting their hypotheses. Here are some frequently observed mistakes:

• Framing Vague Hypotheses : Clarity is vital when defining your hypothesis. A common pitfall involves creating an ambiguous statement which leaves room for multiple interpretations. This hinders precise data collection and analysis.
• Formulating Unfalsifiable Hypotheses : These are statements that cannot be proven false because they don’t connect to observable or measurable variables.
• Targeting Unachievable Results : Often, there is an inclination to develop complex hypotheses expecting groundbreaking findings. However, it’s crucial to limit the scope according to practical constraints and possibilities.
• Ignoring Null Hypothesis : The null hypothesis provides a means of contradiction to the alternative hypothesis being tested, making it essential for any research study.

Tips for avoiding these mistakes

After identifying the commonly made errors when forming a hypothesis, let’s now consider some proactive measures you can adopt:

• Crystallize Your Thoughts : Before you articulate your hypothesis, refine and clarify your ideas first. Define the parameters of your study clearly and ensure your proposition directly aligns with them.
• Keep It Simple : Stick with simplicity as much as possible in describing expected relationships or patterns in your research subject area. Remember: A simpler hypothesis often leads to effective testing.
• Embrace Falsifiability . To avoid making unfalsifiable claims, learn how to craft ‘If – Then’ statements articulately in your define hypothesis process.
• Remember the Null Hypothesis : Always formulate and account for a null hypothesis—a statement that negates the relationship between variables—for robust results validation.

In truth, it takes practice to strike the right balance and formulate a solid, practical hypothesis for your research. With these tips in mind, you’re better equipped to avoid common pitfalls that can compromise the quality of your investigation as they guide your approach when you define hypotheses.

Evaluating and Refining a Hypothesis

Laying out a hypothesis is merely the first stage of an intricate journey. Testing and refining this conjecture is equally pivotal in perfecting your next scientific method of undertaking. This pathway comprises evaluation for validity, and relevance, followed by refinement through research findings.

Methods for Assessing the Validity and Relevance of a Hypothesis

To define a hypothesis of meticulosity, we need to subject it to rigorous scrutiny. Utilizing statistical tests enables you to judge the validity of your hypothesis. Here’s a brief look at some key methods that can assist in assessing your theory:

• Empirical Testing : Conduct experiments or surveys as per the requirements of your study.
• Consistency Check : The hypothesis should remain consistent with other established theories and laws within its field.
• Falsifiability principle : Proposed by Karl Popper, a valid hypothesis must be capable of being proven wrong.

Let me reemphasize here, that relevance plays an integral part too especially when defining hypotheses linked with pragmatics like social sciences or business studies.

A relevant hypothesis will hold significance to not just existing knowledge but also pave the way for future work within the particular area of expertise. It should address gaps in current scientific theories while shedding light on possible solutions.

Ways to Refine and Modify a Hypothesis Based on Research Findings

Our job doesn’t end up on developing an initial proposition; it’s crucial to use findings from our research to refine that preliminary conception further. This essential process breathes life into what was once purely speculative.

While refining your conjecture can sound daunting initially, I assure you it’s nothing more complicated than diagnosing any missing links between your original theory and novel evidence you’ve discovered along this research journey.

If H0 (null hypothesis) contradicts your empirical results, then getting back onto the drafting board becomes necessary for crafting H1 (alternative hypothesis). This scientific cycle of formulating, testing then reformulating the hypotheses can continue till we eventually reach statistically significant results.

Remember, it’s important to be open-minded and responsive towards indications from your research findings. They will guide you intuitively in tweaking your working hypothesis in sync with your target goals.

Hence we must embrace this intricate art of defining a hypothesis while simultaneously embracing its dynamic nature which requires periodic refinement based upon insightful feedback from meticulous research.

Summarizing the Key Points About the Definition and Characteristics of a Hypothesis

Having delved into the concept extensively, we can confidently define a hypothesis as an informed and testable guess or prediction that acts as a guiding light in research studies and scientific investigations. When formulated correctly, it comprises two essential elements: clarity and specificity. It should be free from ambiguity, allowing other researchers to easily understand its proposed idea and the direction the study is heading.

In addition, a robust hypothesis exhibits predictability. As a researcher, you’re not only stating what you think will happen but also defining the variables in your experiment – your assumption confines your investigation’s parameters to make it manageable. Lastly, remember that any meaningful hypothesis must be verifiable — capable of being supported or refuted through data collection and analysis.

Reiterating the Importance of Hypotheses in Scientific Inquiry and Research

This discourse wouldn’t be complete without reaffirming how indispensable hypotheses are within scientific explorations and research inquiries. A conceptualized hypothesis serves as a foundational block upon which every aspect of a research project is built. It directs your observations along assumed patterns, thereby saving time during investigations.

We also need to note that formulating hypotheses promotes critical thinking skills among researchers because they require logical reasoning backed by empirical evidence rather than just empty conjectures.

Henceforth, whether you’re treading through unchartered waters of complex scientific endeavors or conducting social science research with less strict rules for predictions – keeping these insights on “define hypothesis” at hand would surely enhance your journey towards revealing valuable truths.

In essence, cultivating a comprehensive understanding of what constitutes a well-formed hypothesis not only lends credibility to our investigative ventures but also enables us to bring precision, focus, and relevance to our chosen field of exploration. The power lies in its simplistic yet profound ability to guide us from uncertainty towards concrete evidential findings – truly embodying scientific inquiry’s spirit!

Unlock the Power of Visualization with Mind the Graph: Elevate Your Hypothesis to New Heights

As a scientist, your hypothesis is the cornerstone of your research journey. But what if you could take it beyond mere words and equations, and transform it into a visual masterpiece that captivates your audience? Enter Mind the Graph , your ultimate ally in scientific visualization. With our intuitive platform, you can seamlessly translate complex hypotheses into stunning graphs, charts, and illustrations that speak volumes. Whether you are presenting at a conference, publishing a paper, or simply sharing your findings with the world, Mind the Graph empowers you to convey your hypotheses with clarity, precision, and undeniable impact. Join the scientific revolution today and let your hypotheses shine like never before with Mind the Graph.

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• Independent vs. Dependent Variables | Definition & Examples

Independent vs. Dependent Variables | Definition & Examples

Published on February 3, 2022 by Pritha Bhandari . Revised on June 22, 2023.

In research, variables are any characteristics that can take on different values, such as height, age, temperature, or test scores.

Researchers often manipulate or measure independent and dependent variables in studies to test cause-and-effect relationships.

• The independent variable is the cause. Its value is independent of other variables in your study.
• The dependent variable is the effect. Its value depends on changes in the independent variable.

Your independent variable is the temperature of the room. You vary the room temperature by making it cooler for half the participants, and warmer for the other half.

Table of contents

What is an independent variable, types of independent variables, what is a dependent variable, identifying independent vs. dependent variables, independent and dependent variables in research, visualizing independent and dependent variables, other interesting articles, frequently asked questions about independent and dependent variables.

An independent variable is the variable you manipulate or vary in an experimental study to explore its effects. It’s called “independent” because it’s not influenced by any other variables in the study.

Independent variables are also called:

• Explanatory variables (they explain an event or outcome)
• Predictor variables (they can be used to predict the value of a dependent variable)
• Right-hand-side variables (they appear on the right-hand side of a regression equation).

These terms are especially used in statistics , where you estimate the extent to which an independent variable change can explain or predict changes in the dependent variable.

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There are two main types of independent variables.

• Experimental independent variables can be directly manipulated by researchers.
• Subject variables cannot be manipulated by researchers, but they can be used to group research subjects categorically.

Experimental variables

In experiments, you manipulate independent variables directly to see how they affect your dependent variable. The independent variable is usually applied at different levels to see how the outcomes differ.

You can apply just two levels in order to find out if an independent variable has an effect at all.

You can also apply multiple levels to find out how the independent variable affects the dependent variable.

You have three independent variable levels, and each group gets a different level of treatment.

You randomly assign your patients to one of the three groups:

• A low-dose experimental group
• A high-dose experimental group
• A placebo group (to research a possible placebo effect )

A true experiment requires you to randomly assign different levels of an independent variable to your participants.

Random assignment helps you control participant characteristics, so that they don’t affect your experimental results. This helps you to have confidence that your dependent variable results come solely from the independent variable manipulation.

Subject variables

Subject variables are characteristics that vary across participants, and they can’t be manipulated by researchers. For example, gender identity, ethnicity, race, income, and education are all important subject variables that social researchers treat as independent variables.

It’s not possible to randomly assign these to participants, since these are characteristics of already existing groups. Instead, you can create a research design where you compare the outcomes of groups of participants with characteristics. This is a quasi-experimental design because there’s no random assignment. Note that any research methods that use non-random assignment are at risk for research biases like selection bias and sampling bias .

Your independent variable is a subject variable, namely the gender identity of the participants. You have three groups: men, women and other.

Your dependent variable is the brain activity response to hearing infant cries. You record brain activity with fMRI scans when participants hear infant cries without their awareness.

A dependent variable is the variable that changes as a result of the independent variable manipulation. It’s the outcome you’re interested in measuring, and it “depends” on your independent variable.

In statistics , dependent variables are also called:

• Response variables (they respond to a change in another variable)
• Outcome variables (they represent the outcome you want to measure)
• Left-hand-side variables (they appear on the left-hand side of a regression equation)

The dependent variable is what you record after you’ve manipulated the independent variable. You use this measurement data to check whether and to what extent your independent variable influences the dependent variable by conducting statistical analyses.

Based on your findings, you can estimate the degree to which your independent variable variation drives changes in your dependent variable. You can also predict how much your dependent variable will change as a result of variation in the independent variable.

Distinguishing between independent and dependent variables can be tricky when designing a complex study or reading an academic research paper .

A dependent variable from one study can be the independent variable in another study, so it’s important to pay attention to research design .

Here are some tips for identifying each variable type.

Recognizing independent variables

Use this list of questions to check whether you’re dealing with an independent variable:

• Is the variable manipulated, controlled, or used as a subject grouping method by the researcher?
• Does this variable come before the other variable in time?
• Is the researcher trying to understand whether or how this variable affects another variable?

Recognizing dependent variables

Check whether you’re dealing with a dependent variable:

• Is this variable measured as an outcome of the study?
• Is this variable dependent on another variable in the study?
• Does this variable get measured only after other variables are altered?

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Independent and dependent variables are generally used in experimental and quasi-experimental research.

Here are some examples of research questions and corresponding independent and dependent variables.

For experimental data, you analyze your results by generating descriptive statistics and visualizing your findings. Then, you select an appropriate statistical test to test your hypothesis .

The type of test is determined by:

• your variable types
• level of measurement
• number of independent variable levels.

You’ll often use t tests or ANOVAs to analyze your data and answer your research questions.

In quantitative research , it’s good practice to use charts or graphs to visualize the results of studies. Generally, the independent variable goes on the x -axis (horizontal) and the dependent variable on the y -axis (vertical).

The type of visualization you use depends on the variable types in your research questions:

• A bar chart is ideal when you have a categorical independent variable.
• A scatter plot or line graph is best when your independent and dependent variables are both quantitative.

To inspect your data, you place your independent variable of treatment level on the x -axis and the dependent variable of blood pressure on the y -axis.

You plot bars for each treatment group before and after the treatment to show the difference in blood pressure.

If you want to know more about statistics , methodology , or research bias , make sure to check out some of our other articles with explanations and examples.

• Normal distribution
• Degrees of freedom
• Null hypothesis
• Discourse analysis
• Control groups
• Mixed methods research
• Non-probability sampling
• Quantitative research
• Ecological validity

Research bias

• Rosenthal effect
• Implicit bias
• Cognitive bias
• Selection bias
• Negativity bias
• Status quo bias

An independent variable is the variable you manipulate, control, or vary in an experimental study to explore its effects. It’s called “independent” because it’s not influenced by any other variables in the study.

A dependent variable is what changes as a result of the independent variable manipulation in experiments . It’s what you’re interested in measuring, and it “depends” on your independent variable.

In statistics, dependent variables are also called:

Determining cause and effect is one of the most important parts of scientific research. It’s essential to know which is the cause – the independent variable – and which is the effect – the dependent variable.

You want to find out how blood sugar levels are affected by drinking diet soda and regular soda, so you conduct an experiment .

• The type of soda – diet or regular – is the independent variable .
• The level of blood sugar that you measure is the dependent variable – it changes depending on the type of soda.

No. The value of a dependent variable depends on an independent variable, so a variable cannot be both independent and dependent at the same time. It must be either the cause or the effect, not both!

Yes, but including more than one of either type requires multiple research questions .

For example, if you are interested in the effect of a diet on health, you can use multiple measures of health: blood sugar, blood pressure, weight, pulse, and many more. Each of these is its own dependent variable with its own research question.

You could also choose to look at the effect of exercise levels as well as diet, or even the additional effect of the two combined. Each of these is a separate independent variable .

To ensure the internal validity of an experiment , you should only change one independent variable at a time.

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• Derivative of Sec x
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• Local Maxima and Minima in Calculus

Hypothesis is a testable statement that explains what is happening or observed. It proposes the relation between the various participating variables. Hypothesis is also called Theory, Thesis, Guess, Assumption, or Suggestion. Hypothesis creates a structure that guides the search for knowledge.

In this article, we will learn what is hypothesis, its characteristics, types, and examples. We will also learn how hypothesis helps in scientific research.

What is Hypothesis?

A hypothesis is a suggested idea or plan that has little proof, meant to lead to more study. It’s mainly a smart guess or suggested answer to a problem that can be checked through study and trial. In science work, we make guesses called hypotheses to try and figure out what will happen in tests or watching. These are not sure things but rather ideas that can be proved or disproved based on real-life proofs. A good theory is clear and can be tested and found wrong if the proof doesn’t support it.

Hypothesis Meaning

A hypothesis is a proposed statement that is testable and is given for something that happens or observed.

• It is made using what we already know and have seen, and it’s the basis for scientific research.
• A clear guess tells us what we think will happen in an experiment or study.
• It’s a testable clue that can be proven true or wrong with real-life facts and checking it out carefully.
• It usually looks like a “if-then” rule, showing the expected cause and effect relationship between what’s being studied.

Characteristics of Hypothesis

Here are some key characteristics of a hypothesis:

• Testable: An idea (hypothesis) should be made so it can be tested and proven true through doing experiments or watching. It should show a clear connection between things.
• Specific: It needs to be easy and on target, talking about a certain part or connection between things in a study.
• Falsifiable: A good guess should be able to show it’s wrong. This means there must be a chance for proof or seeing something that goes against the guess.
• Logical and Rational: It should be based on things we know now or have seen, giving a reasonable reason that fits with what we already know.
• Predictive: A guess often tells what to expect from an experiment or observation. It gives a guide for what someone might see if the guess is right.
• Concise: It should be short and clear, showing the suggested link or explanation simply without extra confusion.
• Grounded in Research: A guess is usually made from before studies, ideas or watching things. It comes from a deep understanding of what is already known in that area.
• Flexible: A guess helps in the research but it needs to change or fix when new information comes up.
• Relevant: It should be related to the question or problem being studied, helping to direct what the research is about.
• Empirical: Hypotheses come from observations and can be tested using methods based on real-world experiences.

Sources of Hypothesis

Hypotheses can come from different places based on what you’re studying and the kind of research. Here are some common sources from which hypotheses may originate:

• Existing Theories: Often, guesses come from well-known science ideas. These ideas may show connections between things or occurrences that scientists can look into more.
• Observation and Experience: Watching something happen or having personal experiences can lead to guesses. We notice odd things or repeat events in everyday life and experiments. This can make us think of guesses called hypotheses.
• Previous Research: Using old studies or discoveries can help come up with new ideas. Scientists might try to expand or question current findings, making guesses that further study old results.
• Literature Review: Looking at books and research in a subject can help make guesses. Noticing missing parts or mismatches in previous studies might make researchers think up guesses to deal with these spots.
• Problem Statement or Research Question: Often, ideas come from questions or problems in the study. Making clear what needs to be looked into can help create ideas that tackle certain parts of the issue.
• Analogies or Comparisons: Making comparisons between similar things or finding connections from related areas can lead to theories. Understanding from other fields could create new guesses in a different situation.
• Hunches and Speculation: Sometimes, scientists might get a gut feeling or make guesses that help create ideas to test. Though these may not have proof at first, they can be a beginning for looking deeper.
• Technology and Innovations: New technology or tools might make guesses by letting us look at things that were hard to study before.
• Personal Interest and Curiosity: People’s curiosity and personal interests in a topic can help create guesses. Scientists could make guesses based on their own likes or love for a subject.

Types of Hypothesis

Here are some common types of hypotheses:

Simple Hypothesis

Complex hypothesis, directional hypothesis.

• Non-directional Hypothesis

Null Hypothesis (H0)

Alternative hypothesis (h1 or ha), statistical hypothesis, research hypothesis, associative hypothesis, causal hypothesis.

Simple Hypothesis guesses a connection between two things. It says that there is a connection or difference between variables, but it doesn’t tell us which way the relationship goes.

Complex Hypothesis tells us what will happen when more than two things are connected. It looks at how different things interact and may be linked together.

Directional Hypothesis says how one thing is related to another. For example, it guesses that one thing will help or hurt another thing.

Non-Directional Hypothesis

Non-Directional Hypothesis are the one that don’t say how the relationship between things will be. They just say that there is a connection, without telling which way it goes.

Null hypothesis is a statement that says there’s no connection or difference between different things. It implies that any seen impacts are because of luck or random changes in the information.

Alternative Hypothesis is different from the null hypothesis and shows that there’s a big connection or gap between variables. Scientists want to say no to the null hypothesis and choose the alternative one.

Statistical Hypotheis are used in math testing and include making ideas about what groups or bits of them look like. You aim to get information or test certain things using these top-level, common words only.

Research Hypothesis comes from the research question and tells what link is expected between things or factors. It leads the study and chooses where to look more closely.

Associative Hypotheis guesses that there is a link or connection between things without really saying it caused them. It means that when one thing changes, it is connected to another thing changing.

Causal Hypothesis are different from other ideas because they say that one thing causes another. This means there’s a cause and effect relationship between variables involved in the situation. They say that when one thing changes, it directly makes another thing change.

Hypothesis Examples

Following are the examples of hypotheses based on their types:

Simple Hypothesis Example

• Studying more can help you do better on tests.
• Getting more sun makes people have higher amounts of vitamin D.

Complex Hypothesis Example

• How rich you are, how easy it is to get education and healthcare greatly affects the number of years people live.
• A new medicine’s success relies on the amount used, how old a person is who takes it and their genes.

Directional Hypothesis Example

• Drinking more sweet drinks is linked to a higher body weight score.
• Too much stress makes people less productive at work.

Non-directional Hypothesis Example

• Drinking caffeine can affect how well you sleep.
• People often like different kinds of music based on their gender.
• The average test scores of Group A and Group B are not much different.
• There is no connection between using a certain fertilizer and how much it helps crops grow.

Alternative Hypothesis (Ha)

• Patients on Diet A have much different cholesterol levels than those following Diet B.
• Exposure to a certain type of light can change how plants grow compared to normal sunlight.
• The average smarts score of kids in a certain school area is 100.
• The usual time it takes to finish a job using Method A is the same as with Method B.
• Having more kids go to early learning classes helps them do better in school when they get older.
• Using specific ways of talking affects how much customers get involved in marketing activities.
• Regular exercise helps to lower the chances of heart disease.
• Going to school more can help people make more money.
• Playing violent video games makes teens more likely to act aggressively.
• Less clean air directly impacts breathing health in city populations.

Functions of Hypothesis

Hypotheses have many important jobs in the process of scientific research. Here are the key functions of hypotheses:

• Guiding Research: Hypotheses give a clear and exact way for research. They act like guides, showing the predicted connections or results that scientists want to study.
• Formulating Research Questions: Research questions often create guesses. They assist in changing big questions into particular, checkable things. They guide what the study should be focused on.
• Setting Clear Objectives: Hypotheses set the goals of a study by saying what connections between variables should be found. They set the targets that scientists try to reach with their studies.
• Testing Predictions: Theories guess what will happen in experiments or observations. By doing tests in a planned way, scientists can check if what they see matches the guesses made by their ideas.
• Providing Structure: Theories give structure to the study process by arranging thoughts and ideas. They aid scientists in thinking about connections between things and plan experiments to match.
• Focusing Investigations: Hypotheses help scientists focus on certain parts of their study question by clearly saying what they expect links or results to be. This focus makes the study work better.
• Facilitating Communication: Theories help scientists talk to each other effectively. Clearly made guesses help scientists to tell others what they plan, how they will do it and the results expected. This explains things well with colleagues in a wide range of audiences.
• Generating Testable Statements: A good guess can be checked, which means it can be looked at carefully or tested by doing experiments. This feature makes sure that guesses add to the real information used in science knowledge.
• Promoting Objectivity: Guesses give a clear reason for study that helps guide the process while reducing personal bias. They motivate scientists to use facts and data as proofs or disprovals for their proposed answers.
• Driving Scientific Progress: Making, trying out and adjusting ideas is a cycle. Even if a guess is proven right or wrong, the information learned helps to grow knowledge in one specific area.

How Hypothesis help in Scientific Research?

Researchers use hypotheses to put down their thoughts directing how the experiment would take place. Following are the steps that are involved in the scientific method:

• Initiating Investigations: Hypotheses are the beginning of science research. They come from watching, knowing what’s already known or asking questions. This makes scientists make certain explanations that need to be checked with tests.
• Formulating Research Questions: Ideas usually come from bigger questions in study. They help scientists make these questions more exact and testable, guiding the study’s main point.
• Setting Clear Objectives: Hypotheses set the goals of a study by stating what we think will happen between different things. They set the goals that scientists want to reach by doing their studies.
• Designing Experiments and Studies: Assumptions help plan experiments and watchful studies. They assist scientists in knowing what factors to measure, the techniques they will use and gather data for a proposed reason.
• Testing Predictions: Ideas guess what will happen in experiments or observations. By checking these guesses carefully, scientists can see if the seen results match up with what was predicted in each hypothesis.
• Analysis and Interpretation of Data: Hypotheses give us a way to study and make sense of information. Researchers look at what they found and see if it matches the guesses made in their theories. They decide if the proof backs up or disagrees with these suggested reasons why things are happening as expected.
• Encouraging Objectivity: Hypotheses help make things fair by making sure scientists use facts and information to either agree or disagree with their suggested reasons. They lessen personal preferences by needing proof from experience.
• Iterative Process: People either agree or disagree with guesses, but they still help the ongoing process of science. Findings from testing ideas make us ask new questions, improve those ideas and do more tests. It keeps going on in the work of science to keep learning things.

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Summary – Hypothesis

A hypothesis is a testable statement serving as an initial explanation for phenomena, based on observations, theories, or existing knowledge. It acts as a guiding light for scientific research, proposing potential relationships between variables that can be empirically tested through experiments and observations. The hypothesis must be specific, testable, falsifiable, and grounded in prior research or observation, laying out a predictive, if-then scenario that details a cause-and-effect relationship. It originates from various sources including existing theories, observations, previous research, and even personal curiosity, leading to different types, such as simple, complex, directional, non-directional, null, and alternative hypotheses, each serving distinct roles in research methodology. The hypothesis not only guides the research process by shaping objectives and designing experiments but also facilitates objective analysis and interpretation of data, ultimately driving scientific progress through a cycle of testing, validation, and refinement.

FAQs on Hypothesis

What is a hypothesis.

A guess is a possible explanation or forecast that can be checked by doing research and experiments.

What are Components of a Hypothesis?

The components of a Hypothesis are Independent Variable, Dependent Variable, Relationship between Variables, Directionality etc.

What makes a Good Hypothesis?

Testability, Falsifiability, Clarity and Precision, Relevance are some parameters that makes a Good Hypothesis

Can a Hypothesis be Proven True?

You cannot prove conclusively that most hypotheses are true because it’s generally impossible to examine all possible cases for exceptions that would disprove them.

How are Hypotheses Tested?

Hypothesis testing is used to assess the plausibility of a hypothesis by using sample data

Can Hypotheses change during Research?

Yes, you can change or improve your ideas based on new information discovered during the research process.

What is the Role of a Hypothesis in Scientific Research?

Hypotheses are used to support scientific research and bring about advancements in knowledge.

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• Scientific Methods

What is Hypothesis?

We have heard of many hypotheses which have led to great inventions in science. Assumptions that are made on the basis of some evidence are known as hypotheses. In this article, let us learn in detail about the hypothesis and the type of hypothesis with examples.

A hypothesis is an assumption that is made based on some evidence. This is the initial point of any investigation that translates the research questions into predictions. It includes components like variables, population and the relation between the variables. A research hypothesis is a hypothesis that is used to test the relationship between two or more variables.

Characteristics of Hypothesis

Following are the characteristics of the hypothesis:

• The hypothesis should be clear and precise to consider it to be reliable.
• If the hypothesis is a relational hypothesis, then it should be stating the relationship between variables.
• The hypothesis must be specific and should have scope for conducting more tests.
• The way of explanation of the hypothesis must be very simple and it should also be understood that the simplicity of the hypothesis is not related to its significance.

Sources of Hypothesis

Following are the sources of hypothesis:

• The resemblance between the phenomenon.
• Observations from past studies, present-day experiences and from the competitors.
• Scientific theories.
• General patterns that influence the thinking process of people.

Types of Hypothesis

There are six forms of hypothesis and they are:

• Simple hypothesis
• Complex hypothesis
• Directional hypothesis
• Non-directional hypothesis
• Null hypothesis
• Associative and casual hypothesis

Simple Hypothesis

It shows a relationship between one dependent variable and a single independent variable. For example – If you eat more vegetables, you will lose weight faster. Here, eating more vegetables is an independent variable, while losing weight is the dependent variable.

Complex Hypothesis

It shows the relationship between two or more dependent variables and two or more independent variables. Eating more vegetables and fruits leads to weight loss, glowing skin, and reduces the risk of many diseases such as heart disease.

Directional Hypothesis

It shows how a researcher is intellectual and committed to a particular outcome. The relationship between the variables can also predict its nature. For example- children aged four years eating proper food over a five-year period are having higher IQ levels than children not having a proper meal. This shows the effect and direction of the effect.

Non-directional Hypothesis

It is used when there is no theory involved. It is a statement that a relationship exists between two variables, without predicting the exact nature (direction) of the relationship.

Null Hypothesis

It provides a statement which is contrary to the hypothesis. It’s a negative statement, and there is no relationship between independent and dependent variables. The symbol is denoted by “H O ”.

Associative and Causal Hypothesis

Associative hypothesis occurs when there is a change in one variable resulting in a change in the other variable. Whereas, the causal hypothesis proposes a cause and effect interaction between two or more variables.

Examples of Hypothesis

Following are the examples of hypotheses based on their types:

• Consumption of sugary drinks every day leads to obesity is an example of a simple hypothesis.
• All lilies have the same number of petals is an example of a null hypothesis.
• If a person gets 7 hours of sleep, then he will feel less fatigue than if he sleeps less. It is an example of a directional hypothesis.

Functions of Hypothesis

Following are the functions performed by the hypothesis:

• Hypothesis helps in making an observation and experiments possible.
• It becomes the start point for the investigation.
• Hypothesis helps in verifying the observations.
• It helps in directing the inquiries in the right direction.

How will Hypothesis help in the Scientific Method?

Researchers use hypotheses to put down their thoughts directing how the experiment would take place. Following are the steps that are involved in the scientific method:

• Formation of question
• Doing background research
• Creation of hypothesis
• Designing an experiment
• Collection of data
• Result analysis
• Summarizing the experiment
• Communicating the results

Frequently Asked Questions – FAQs

What is hypothesis.

A hypothesis is an assumption made based on some evidence.

Give an example of simple hypothesis?

What are the types of hypothesis.

Types of hypothesis are:

• Associative and Casual hypothesis

State true or false: Hypothesis is the initial point of any investigation that translates the research questions into a prediction.

Define complex hypothesis..

A complex hypothesis shows the relationship between two or more dependent variables and two or more independent variables.

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