scoping review vs systematic literature review

Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach

Affiliations.

• 1 The Joanna Briggs Institute, The University of Adelaide, 55 King William Road, North Adelaide, 5005, South Australia. [email protected].
• 2 The Joanna Briggs Institute, The University of Adelaide, 55 King William Road, North Adelaide, 5005, South Australia.
• PMID: 30453902
• PMCID: PMC6245623
• DOI: 10.1186/s12874-018-0611-x

Background: Scoping reviews are a relatively new approach to evidence synthesis and currently there exists little guidance regarding the decision to choose between a systematic review or scoping review approach when synthesising evidence. The purpose of this article is to clearly describe the differences in indications between scoping reviews and systematic reviews and to provide guidance for when a scoping review is (and is not) appropriate.

Results: Researchers may conduct scoping reviews instead of systematic reviews where the purpose of the review is to identify knowledge gaps, scope a body of literature, clarify concepts or to investigate research conduct. While useful in their own right, scoping reviews may also be helpful precursors to systematic reviews and can be used to confirm the relevance of inclusion criteria and potential questions.

Conclusions: Scoping reviews are a useful tool in the ever increasing arsenal of evidence synthesis approaches. Although conducted for different purposes compared to systematic reviews, scoping reviews still require rigorous and transparent methods in their conduct to ensure that the results are trustworthy. Our hope is that with clear guidance available regarding whether to conduct a scoping review or a systematic review, there will be less scoping reviews being performed for inappropriate indications better served by a systematic review, and vice-versa.

Keywords: Evidence-based healthcare; Scoping review; Systematic review.

• Choice Behavior* / physiology
• Decision Making / physiology
• Evidence-Based Medicine / methods
• Evidence-Based Medicine / standards
• Guidelines as Topic* / standards
• Publications / classification
• Publications / standards
• Research Design
• Research Personnel
• Review Literature as Topic*
• Systematic Reviews as Topic*

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The difference between a systematic review & scoping review

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Home | Blog | Best Practice | The difference between a systematic review & scoping review

Covidence explains the two study designs

Research: there’s a lot of it! So much, in fact, that keeping track gets harder by the day – even within a narrow specialism or subject area. 

Evidence synthesis is a type of secondary research that brings together information from a range of sources to inform decision making. It attempts to review the research in a rigorous and systematic way so that it can be used to support evidence-based practice.

Within evidence synthesis, different types of reviews have emerged to tackle the huge task of summarising the literature. It can be hard to keep track of these too! 

What’s the deal with scoping reviews, for example? How do they differ from systematic reviews? Both are types of evidence synthesis and each has a specific use. Let’s look at these two review types in turn to pick up on the key similarities and differences 🕵🏾‍♀️ . 

1. What is a systematic review?

Systematic reviews ask a specific question about the effectiveness of a treatment and answer it by summarising evidence that meets a set of pre-specified criteria. 

The process starts with a research question and a protocol or research plan💡. A review team searches for studies to answer the question using a highly sensitive search strategy. The retrieved studies are then screened for eligibility using the inclusion and exclusion criteria (this is done by at least two people working independently 👩🏻‍💻👨🏾‍💻). Next, the reviewers extract the relevant data and assess the quality of the included studies. Finally, the review team synthesises the extracted study data and presents the results. The process is shown in figure 2.

‘Systematic’ means that the methods used to search for and analyse the data are

transparent, reproducible and defined before searching begins. Systematic reviews strive to be as thorough and rigorous as possible to minimise the bias that would result from cherry-picking studies in a non-systematic way. 

When is it appropriate to do a systematic review?

If you have a clinical question about the effectiveness of a particular treatment or treatments, you could answer it by conducting a systematic review. The first systematic review published by Cochrane assessed the effectiveness of antenatal corticosteroids for accelerating fetal lung maturation in women at risk of preterm birth . Systematic review evidence is used in the development of guidelines by organisations such as the World Health Organization and the Agency for Healthcare Research and Quality in the US.

What guidelines should a systematic review follow?

The PRISMA guidelines set out the items that should be included in the reporting of a systematic review.

How can I get help with my systematic review?

Covidence is an online tool that saves time on the screening, data extraction and quality assessment stages of your systematic review 👍. Its simple workflows enable review teams to collaborate and track their progress easily and reliably. Covidence automatically populates a PRISMA flow diagram for each review. The flow diagram documents the decisions on the inclusion and exclusion of studies and can be added to the results section of the review.

2. What is a scoping review?

Systematic reviews are resource intensive. To find out whether starting work on one is a good idea, some researchers conduct a scoping review first to find out more about the body of evidence in a particular topic area. 

Scoping reviews are exploratory, and they typically address a broad question. Researchers conduct them to assess the extent of the available evidence, to organise it into groups and to highlight gaps. Sometimes scoping reviews are also used to decide whether or not it would be useful to conduct a systematic review 🤔.

The scoping review process is shown in figure 3. Like systematic reviews, scoping reviews define eligibility criteria, search the literature, screen the results and select evidence for inclusion. The data extraction stage, in which the review team creates a descriptive summary of the evidence, is called ‘charting’ 📊. The JBI Manual for evidence synthesis recommends that scoping reviews extract the following study information:

When is it appropriate to do a scoping review?

If you want to establish the full range of treatments in a particular area of health care or explore the health of a specific population, you could perform a scoping review. A recent scoping review looked at the health of adolescents in detention . The results of a scoping review can give review teams the information they need to be specific when they formulate their systematic review question 🎯. The scoping review might also give an indication of how long it would take to complete the systematic review. 

What guidelines should a scoping review follow?

The PRISMA extension for scoping reviews is a list of 20 essential reporting items for review teams when completing a scoping review.

How can I get help with my scoping review?

Scoping reviews can generate a large volume of citations, which can be a daunting task! Covidence supports review teams to screen citations quickly and efficiently. It can also help teams to set up standardised charting forms and ensure a consistent and rigorous approach to decision making throughout the project 😅.

Interest in systematic reviews and scoping reviews has grown rapidly in recent years. Review methods are evolving constantly as researchers find new ways to meet the challenge of synthesising the evidence. Whether you’re planning a systematic review, a scoping review, or both, Covidence can help you and your team keep your project on track. 

Sign up for a free trial today!

Laura Mellor. Portsmouth, UK

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• Open access
• Published: 19 November 2018

Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach

• Zachary Munn   ORCID: orcid.org/0000-0002-7091-5842 1 ,
• Micah D. J. Peters 1 ,
• Cindy Stern 1 ,
• Catalin Tufanaru 1 ,
• Alexa McArthur 1 &
• Edoardo Aromataris 1  

BMC Medical Research Methodology volume  18 , Article number:  143 ( 2018 ) Cite this article

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Scoping reviews are a relatively new approach to evidence synthesis and currently there exists little guidance regarding the decision to choose between a systematic review or scoping review approach when synthesising evidence. The purpose of this article is to clearly describe the differences in indications between scoping reviews and systematic reviews and to provide guidance for when a scoping review is (and is not) appropriate.

Researchers may conduct scoping reviews instead of systematic reviews where the purpose of the review is to identify knowledge gaps, scope a body of literature, clarify concepts or to investigate research conduct. While useful in their own right, scoping reviews may also be helpful precursors to systematic reviews and can be used to confirm the relevance of inclusion criteria and potential questions.

Conclusions

Scoping reviews are a useful tool in the ever increasing arsenal of evidence synthesis approaches. Although conducted for different purposes compared to systematic reviews, scoping reviews still require rigorous and transparent methods in their conduct to ensure that the results are trustworthy. Our hope is that with clear guidance available regarding whether to conduct a scoping review or a systematic review, there will be less scoping reviews being performed for inappropriate indications better served by a systematic review, and vice-versa.

Peer Review reports

Systematic reviews in healthcare began to appear in publication in the 1970s and 1980s [ 1 , 2 ]. With the emergence of groups such as Cochrane and the Joanna Briggs Institute (JBI) in the 1990s [ 3 ], reviews have exploded in popularity both in terms of the number conducted [ 1 ], and their uptake to inform policy and practice. Today, systematic reviews are conducted for a wide range of purposes across diverse fields of inquiry, different evidence types and for different questions [ 4 ]. More recently, the field of evidence synthesis has seen the emergence of scoping reviews, which are similar to systematic reviews in that they follow a structured process, however they are performed for different reasons and have some key methodological differences [ 5 , 6 , 7 , 8 ]. Scoping reviews are now seen as a valid approach in those circumstances where systematic reviews are unable to meet the necessary objectives or requirements of knowledge users. There now exists clear guidance regarding the definition of scoping reviews, how to conduct scoping reviews and the steps involved in the scoping review process [ 6 , 8 ]. However, the guidance regarding the key indications or reasons why reviewers may choose to follow a scoping review approach is not as straightforward, with scoping reviews often conducted for purposes that do not align with the original indications as proposed by Arksey and O’Malley [ 5 , 6 , 7 , 8 , 9 , 10 ]. As editors and peer reviewers for various journals we have noticed that there is inconsistency and confusion regarding the indications for scoping reviews and a lack of clarity for authors regarding when a scoping review should be performed as opposed to a systematic review. The purpose of this article is to provide practical guidance for reviewers on when to perform a systematic review or a scoping review, supported with some key examples.

Indications for systematic reviews

Systematic reviews can be broadly defined as a type of research synthesis that are conducted by review groups with specialized skills, who set out to identify and retrieve international evidence that is relevant to a particular question or questions and to appraise and synthesize the results of this search to inform practice, policy and in some cases, further research [ 11 , 12 , 13 ]. According to the Cochrane handbook, a systematic review ‘uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made.’ [ 14 ] Systematic reviews follow a structured and pre-defined process that requires rigorous methods to ensure that the results are both reliable and meaningful to end users. These reviews may be considered the pillar of evidence-based healthcare [ 15 ] and are widely used to inform the development of trustworthy clinical guidelines [ 11 , 16 , 17 ].

A systematic review may be undertaken to confirm or refute whether or not current practice is based on relevant evidence, to establish the quality of that evidence, and to address any uncertainty or variation in practice that may be occurring. Such variations in practice may be due to conflicting evidence and undertaking a systematic review should (hopefully) resolve such conflicts. Conducting a systematic review may also identify gaps, deficiencies, and trends in the current evidence and can help underpin and inform future research in the area. Systematic reviews can be used to produce statements to guide clinical decision-making, the delivery of care, as well as policy development [ 12 ]. Broadly, indications for systematic reviews are as follows [ 4 ]:

Uncover the international evidence

Confirm current practice/ address any variation/ identify new practices

Identify and inform areas for future research

Identify and investigate conflicting results

Produce statements to guide decision-making

Despite the utility of systematic reviews to address the above indications, there are cases where systematic reviews are unable to meet the necessary objectives or requirements of knowledge users or where a methodologically robust and structured preliminary searching and scoping activity may be useful to inform the conduct of the systematic reviews. As such, scoping reviews (which are also sometimes called scoping exercises/scoping studies) [ 8 ] have emerged as a valid approach with rather different indications to those for systematic reviews. It is important to note here that other approaches to evidence synthesis have also emerged, including realist reviews, mixed methods reviews, concept analyses and others [ 4 , 18 , 19 , 20 ]. This article focuses specifically on the choice between a systematic review or scoping review approach.

Indications for scoping reviews

True to their name, scoping reviews are an ideal tool to determine the scope or coverage of a body of literature on a given topic and give clear indication of the volume of literature and studies available as well as an overview (broad or detailed) of its focus. Scoping reviews are useful for examining emerging evidence when it is still unclear what other, more specific questions can be posed and valuably addressed by a more precise systematic review [ 21 ]. They can report on the types of evidence that address and inform practice in the field and the way the research has been conducted.

The general purpose for conducting scoping reviews is to identify and map the available evidence [ 5 , 22 ]. Arskey and O’Malley, authors of the seminal paper describing a framework for scoping reviews, provided four specific reasons why a scoping review may be conducted [ 5 , 6 , 7 , 22 ]. Soon after, Levac, Colquhoun and O’Brien further clarified and extended this original framework [ 7 ]. These authors acknowledged that at the time, there was no universally recognized definition of scoping reviews nor a commonly acknowledged purpose or indication for conducting them. In 2015, a methodological working group of the JBI produced formal guidance for conducting scoping reviews [ 6 ]. However, we have not previously addressed and expanded upon the indications for scoping reviews. Below, we build upon previously described indications and suggest the following purposes for conducting a scoping review:

To identify the types of available evidence in a given field

To clarify key concepts/ definitions in the literature

To examine how research is conducted on a certain topic or field

To identify key characteristics or factors related to a concept

As a precursor to a systematic review.

To identify and analyse knowledge gaps

Deciding between a systematic review and a scoping review approach

Authors deciding between the systematic review or scoping review approach should carefully consider the indications discussed above for each synthesis type and determine exactly what question they are asking and what purpose they are trying to achieve with their review. We propose that the most important consideration is whether or not the authors wish to use the results of their review to answer a clinically meaningful question or provide evidence to inform practice. If the authors have a question addressing the feasibility, appropriateness, meaningfulness or effectiveness of a certain treatment or practice, then a systematic review is likely the most valid approach [ 11 , 23 ]. However, authors do not always wish to ask such single or precise questions, and may be more interested in the identification of certain characteristics/concepts in papers or studies, and in the mapping, reporting or discussion of these characteristics/concepts. In these cases, a scoping review is the better choice.

As scoping reviews do not aim to produce a critically appraised and synthesised result/answer to a particular question, and rather aim to provide an overview or map of the evidence. Due to this, an assessment of methodological limitations or risk of bias of the evidence included within a scoping review is generally not performed (unless there is a specific requirement due to the nature of the scoping review aim) [ 6 ]. Given this assessment of bias is not conducted, the implications for practice (from a clinical or policy making point of view) that arise from a scoping review are quite different compared to those of a systematic review. In some cases, there may be no need or impetus to make implications for practice and if there is a need to do so, these implications may be significantly limited in terms of providing concrete guidance from a clinical or policy making point of view. Conversely, when we compare this to systematic reviews, the provision of implications for practice is a key feature of systematic reviews and is recommended in reporting guidelines for systematic reviews [ 13 ].

Exemplars for different scoping review indications

In the following section, we elaborate on each of the indications listed for scoping reviews and provide a number of examples for authors considering a scoping review approach.

Scoping reviews that seek to identify the types of evidence in a given field share similarities with evidence mapping activities as explained by Bragge and colleagues in a paper on conducting scoping research in broad topic areas [ 24 ]. Chambers and colleagues [ 25 ] conducted a scoping review in order to identify current knowledge translation resources (and any evaluations of them) that use, adapt and present findings from systematic reviews to suit the needs of policy makers. Following a comprehensive search across a range of databases, organizational websites and conference abstract repositories based upon predetermined inclusion criteria, the authors identified 20 knowledge translation resources which they classified into three different types (overviews, summaries and policy briefs) as well as seven published and unpublished evaluations. The authors concluded that evidence synthesists produce a range of resources to assist policy makers to transfer and utilize the findings of systematic reviews and that focussed summaries are the most common. Similarly, a scoping review was conducted by Challen and colleagues [ 26 ] in order to determine the types of available evidence identifying the source and quality of publications and grey literature for emergency planning. A comprehensive set of databases and websites were investigated and 1603 relevant sources of evidence were identified mainly addressing emergency planning and response with fewer sources concerned with hazard analysis, mitigation and capability assessment. Based on the results of the review, the authors concluded that while there is a large body of evidence in the field, issues with its generalizability and validity are as yet largely unknown and that the exact type and form of evidence that would be valuable to knowledge users in the field is not yet understood.

To clarify key concepts/definitions in the literature

Scoping reviews are often performed to examine and clarify definitions that are used in the literature. A scoping review by Schaink and colleagues 27 was performed to investigate how the notion of “patient complexity” had been defined, classified, and understood in the existing literature. A systematic search of healthcare databases was conducted. Articles were assessed to determine whether they met the inclusion criteria and the findings of included articles were grouped into five health dimensions. An overview of how complexity has been described was presented, including the varying definitions and interpretations of the term. The results of the scoping review enabled the authors to then develop a complexity framework or model to assist in defining and understanding patient complexity [ 27 ].

Hines et al. [ 28 ] provide a further example where a scoping review has been conducted to define a concept, in this case the condition bronchopulmonary dysplasia. The authors revealed significant variation in how the condition was defined across the literature, prompting the authors to call for a ‘comprehensive and evidence-based definition’. [ 28 ]

To examine how research is conducted on a certain topic

Scoping reviews can be useful tools to investigate the design and conduct of research on a particular topic. A scoping review by Callary and colleagues 29 investigated the methodological design of studies assessing wear of a certain type of hip replacement (highly crosslinked polyethylene acetabular components) [ 29 ]. The aim of the scoping review was to survey the literature to determine how data pertinent to the measurement of hip replacement wear had been reported in primary studies and whether the methods were similar enough to allow for comparison across studies. The scoping review revealed that the methods to assess wear (radiostereometric analysis) varied significantly with many different approaches being employed amongst the investigators. The results of the scoping review led to the authors recommending enhanced standardization in measurements and methods for future research in this field [ 29 ].

There are other examples of scoping reviews investigating research methodology, with perhaps the most pertinent examples being two recent scoping reviews of scoping review methods [ 9 , 10 ]. Both of these scoping reviews investigated how scoping reviews had been reported and conducted, with both advocating for a need for clear guidance to improve standardization of methods [ 9 , 10 ]. Similarly, a scoping review investigating methodology was conducted by Tricco and colleagues 30 on rapid review methods that have been evaluated, compared, used or described in the literature. A variety of rapid review approaches were identified with many instances of poor reporting identified. The authors called for prospective studies to compare results presented by rapid reviews versus systematic reviews.

Scoping reviews can be conducted to identify and examine characteristics or factors related to a particular concept. Harfield and colleagues (2015) conducted a scoping review to identify the characteristics of indigenous primary healthcare service delivery models [ 30 , 31 , 32 ]. A systematic search was conducted, followed by screening and study selection. Once relevant studies had been identified, a process of data extraction commenced to extract characteristics referred to in the included papers. Over 1000 findings were eventually grouped into eight key factors (accessible health services, community participation, culturally appropriate and skilled workforce, culture, continuous quality improvement, flexible approaches to care, holistic health care, self-determination and empowerment). The results of this scoping review have been able to inform a best practice model for indigenous primary healthcare services.

Scoping reviews conducted as precursors to systematic reviews may enable authors to identify the nature of a broad field of evidence so that ensuing reviews can be assured of locating adequate numbers of relevant studies for inclusion. They also enable the relevant outcomes and target group or population for example for a particular intervention to be identified. This can have particular practical benefits for review teams undertaking reviews on less familiar topics and can assist the team to avoid undertaking an “empty” review [ 33 ]. Scoping reviews of this kind may help reviewers to develop and confirm their a priori inclusion criteria and ensure that the questions to be posed by their subsequent systematic review are able to be answered by available, relevant evidence. In this way, systematic reviews are able to be underpinned by a preliminary and evidence-based scoping stage.

A scoping review commissioned by the United Kingdom Department for International Development was undertaken to determine the scope and nature of literature on people’s experiences of microfinance. The results of this scoping review were used to inform the development of targeted systematic review questions that focussed upon areas of particular interest [ 34 ].

In their recent scoping review on the conduct and reporting of scoping reviews, Tricco and colleagues 10 reveal only 12% of scoping reviews contained recommendations for the development of ensuing systematic reviews, suggesting that the majority of scoping review authors do not conduct scoping reviews as a precursor to future systematic reviews.

To identify and analyze gaps in the knowledge base

Scoping reviews are rarely solely conducted to simply identify and analyze gaps present in a given knowledge base, as examination and presentation of what hasn’t been investigated or reported generally requires exhaustive examination of all of what is available. In any case, because scoping reviews tend to be a useful approach for reviewing evidence rapidly in emerging fields or topics, identification and analysis of knowledge gaps is a common and valuable indication for conducting a scoping review. A scoping review was recently conducted to review current research and identify knowledge gaps on the topic of “occupational balance”, or the balance of work, rest, sleep, and play [ 35 ]. Following a systematic search across a range of relevant databases, included studies were selected and in line with predetermined inclusion criteria, were described and mapped to provide both an overall picture of the current state of the evidence in the field and to identify and highlight knowledge gaps in the area. The results of the scoping review allowed the authors to illustrate several research ‘gaps’, including the absence of studies conducted outside of western societies, the lack of knowledge around peoples’ levels of occupational balance, as well as a dearth of evidence regarding how occupational balance may be enhanced. As with other scoping reviews focussed upon identifying and analyzing knowledge gaps, results such as these allow for the identification of future research initiatives.

Scoping reviews are now seen as a valid review approach for certain indications. A key difference between scoping reviews and systematic reviews is that in terms of a review question, a scoping review will have a broader “scope” than traditional systematic reviews with correspondingly more expansive inclusion criteria. In addition, scoping reviews differ from systematic reviews in their overriding purpose. We have previously recommended the use of the PCC mnemonic (Population, Concept and Context) to guide question development [ 36 ]. The importance of clearly defining the key questions and objectives of a scoping review has been discussed previously by one of the authors, as a lack of clarity can result in difficulties encountered later on in the review process [ 36 ].

Considering their differences from systematic reviews, scoping reviews should still not be confused with traditional literature reviews. Traditional literature reviews have been used as a means to summarise various publications or research on a particular topic for many years. In these traditional reviews, authors examine research reports in addition to conceptual or theoretical literature that focuses on the history, importance, and collective thinking around a topic, issue or concept. These types of reviews can be considered subjective, due to their substantial reliance on the author’s pre-exiting knowledge and experience and as they do not normally present an unbiased, exhaustive and systematic summary of a topic [ 12 ]. Regardless of some of these limitations, traditional literature reviews may still have some use in terms of providing an overview of a topic or issue. Scoping reviews provide a useful alternative to literature reviews when clarification around a concept or theory is required. If traditional literature reviews are contrasted with scoping reviews, the latter [ 6 ]:

Are informed by an a priori protocol

Are systematic and often include exhaustive searching for information

Aim to be transparent and reproducible

Include steps to reduce error and increase reliability (such as the inclusion of multiple reviewers)

Ensure data is extracted and presented in a structured way

Another approach to evidence synthesis that has emerged recently is the production of evidence maps [ 37 ]. The purpose of these evidence maps is similar to scoping reviews to identify and analyse gaps in the knowledge base [ 37 , 38 ]. In fact, most evidence mapping articles cite seminal scoping review guidance for their methods [ 38 ]. The two approaches therefore have many similarities, with perhaps the most prominent difference being the production of a visual database or schematic (i.e. map) which assists the user in interpreting where evidence exists and where there are gaps [ 38 ]. As Miake-Lye states, at this stage ‘it is difficult to determine where one method ends and the other begins.’ [ 38 ] Both approaches may be valid when the indication is for determining the extent of evidence on a particular topic, particularly when highlighting gaps in the research.

A further popular method to define and scope concepts, particularly in nursing, is through the conduct of a concept analysis [ 39 , 40 , 41 , 42 ]. Formal concept analysis is ‘a process whereby concepts are logically and systematically investigated to form clear and rigorously constructed conceptual definitions,’ [ 42 ] which is similar to scoping reviews where the indication is to clarify concepts in the literature. There is limited methodological guidance on how to conduct a concept analysis and recently they have been critiqued for having no impact on practice [ 39 ]. In our opinion, scoping reviews (where the purpose is to systematically investigate a concept in the literature) offer a methodologically rigorous alternative to concept analysis with their results perhaps being more useful to inform practice.

Comparing and contrasting the characteristics of traditional literature reviews, scoping reviews and systematic reviews may help clarify the true essence of these different types of reviews (see Table 1 ).

Rapid reviews are another emerging type of evidence synthesis and a substantial amount of literature have addressed these types of reviews [ 43 , 44 , 45 , 46 , 47 ]. There are various definitions for rapid reviews, and for simplification purposes, we define these review types as ‘systematic reviews with shortcuts.’ In this paper, we have not discussed the choice between a rapid or systematic review approach as we are of the opinion that perhaps the major consideration for conducting a rapid review (as compared to a systematic or scoping review) is not the purpose/question itself, but the feasibility of conducting a full review given financial/resource limitations and time pressures. As such, a rapid review could potentially be conducted for any of the indications listed above for the scoping or systematic review, whilst shortening or skipping entirely some steps in the standard systematic or scoping review process.

There is some overlap across the six listed purposes for conducting a scoping review described in this paper. For example, it is logical to presume that if a review group were aiming to identify the types of available evidence in a field they would also be interested in identifying and analysing gaps in the knowledge base. Other combinations of purposes for scoping reviews would also make sense for certain questions/aims. However, we have chosen to list them as discrete reasons in this paper in an effort to provide some much needed clarity on the appropriate purposes for conducting scoping reviews. As such, scoping review authors should not interpret our list of indications as a discrete list where only one purpose can be identified.

It is important to mention some potential abuses of scoping reviews. Reviewers may conduct a scoping review as an alternative to a systematic review in order to avoid the critical appraisal stage of the review and expedite the process, thinking that a scoping review may be easier than a systematic review to conduct. Other reviewers may conduct a scoping review in order to ‘map’ the literature when there is no obvious need for ‘mapping’ in this particular subject area. Others may conduct a scoping review with very broad questions as an alternative to investing the time and effort required to craft the necessary specific questions required for undertaking a systematic review. In these cases, scoping reviews are not appropriate and authors should refer to our guidance regarding whether they should be conducting a systematic review instead.

This article provides some clarification on when to conduct a scoping review as compared to a systematic review and clear guidance on the purposes for conducting a scoping review. We hope that this paper will provide a useful addition to this evolving methodology and encourage others to review, modify and build upon these indications as the approach matures. Further work in scoping review methods is required, with perhaps the most important advancement being the recent development of an extension to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for scoping reviews [ 48 ] and the development of software and training programs to support these reviews [ 49 , 50 ]. As the methodology advances, guidance for scoping reviews (such as that included in the Joanna Briggs Institute Reviewer’s Manual) will require revision, refining and updating.

Scoping reviews are a useful tool in the ever increasing arsenal of evidence synthesis approaches. Researchers may preference the conduct of a scoping review over a systematic review where the purpose of the review is to identify knowledge gaps, scope a body of literature, clarify concepts, investigate research conduct, or to inform a systematic review. Although conducted for different purposes compared to systematic reviews, scoping reviews still require rigorous and transparent methods in their conduct to ensure that the results are trustworthy. Our hope is that with clear guidance available regarding whether to conduct a scoping review or a systematic review, there will be less scoping reviews being performed for inappropriate indications better served by a systematic review, and vice-versa.

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ZM: Led the development of this paper and conceptualised the idea for a paper on indications for scoping reviews. Provided final approval for submission. MP: Contributed conceptually to the paper and wrote sections of the paper. Provided final approval for submission. CS: Contributed conceptually to the paper and wrote sections of the paper. Provided final approval for submission. CT: Contributed conceptually to the paper and wrote sections of the paper. Provided final approval for submission. AM: Contributed conceptually to the paper and reviewed and provided feedback on all drafts. Provided final approval for submission. EA: Contributed conceptually to the paper and reviewed and provided feedback on all drafts. Provided approval and encouragement for the work to proceed. Provided final approval for submission.

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Munn, Z., Peters, M.D.J., Stern, C. et al. Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Med Res Methodol 18 , 143 (2018). https://doi.org/10.1186/s12874-018-0611-x

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• Systematic review
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BMC Medical Research Methodology

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• Research Guides
• Reviewing Research: Literature Reviews, Scoping Reviews, Systematic Reviews
• Differentiating the Three Review Types

Reviewing Research: Literature Reviews, Scoping Reviews, Systematic Reviews: Differentiating the Three Review Types

• Framework, Protocol, and Writing Steps
• Working with Keywords/Subject Headings
• Citing Research

The Differences in the Review Types

Grant, M.J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies. H ealth Information & Libraries Journal , 26: 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x   The objective of this study is to provide descriptive insight into the most common types of reviews, with illustrative examples from health and health information domains.

• What Type of Review is Right for you (Cornell University)

Literature Reviews

Literature Review: it is a product and a process.

As a product , it is a carefully written examination, interpretation, evaluation, and synthesis of the published literature related to your topic. It focuses on what is known about your topic and what methodologies, models, theories, and concepts have been applied to it by others.

The process is what is involved in conducting a review of the literature.

• It is ongoing
• It is iterative (repetitive)
• It involves searching for and finding relevant literature.
• It includes keeping track of your references and preparing and formatting them for the bibliography of your thesis

• Literature Reviews (University of North Carolina at Chapel Hill) This handout will explain what literature reviews are and offer insights into the form and construction of literature reviews in the humanities, social sciences, and sciences.

Scoping Reviews

Scoping reviews are a " preliminary assessment of potential size and scope of available research literature . Aims to identify nature and extent of research evidence (usually including ongoing research)." Grant and Booth (2009).

Scoping reviews are not mapping reviews: Scoping reviews are more topic based and mapping reviews are more question based.

• examining emerging evidence when specific questions are unclear - clarify definitions and conceptual boundaries
• identify and map the available evidence
• a scoping review is done prior to a systematic review
• to summarize and disseminate research findings in the research literature
• identify gaps with the intention of resolution by future publications

• Scoping review timeframe and limitations (Touro College of Pharmacy

Systematic Reviews

Many evidence-based disciplines use ‘systematic reviews," this type of review is a specific methodology that aims to comprehensively identify all relevant studies on a specific topic, and to select appropriate studies based on explicit criteria . ( https://cebma.org/faq/what-is-a-systematic-review/ )

• clearly defined search criteria
• an explicit reproducible methodology
• a systematic search of the literature with the defined criteria met
• assesses validity of the findings - no risk of bias
• a comprehensive report on the findings, apparent transparency in the results

• Better evidence for a better world Browsable collection of systematic reviews
• Systematic Reviews in the Health Sciences by Molly Maloney Last Updated May 7, 2024 566 views this year
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Systematic, Scoping, and Other Literature Reviews: Overview

• Project Planning

What Is a Systematic Review?

Regular literature reviews are simply summaries of the literature on a particular topic. A systematic review, however, is a comprehensive literature review conducted to answer a specific research question. Authors of a systematic review aim to find, code, appraise, and synthesize all of the previous research on their question in an unbiased and well-documented manner. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) outline the minimum amount of information that needs to be reported at the conclusion of a systematic review project. 

Other types of what are known as "evidence syntheses," such as scoping, rapid, and integrative reviews, have varying methodologies. While systematic reviews originated with and continue to be a popular publication type in medicine and other health sciences fields, more and more researchers in other disciplines are choosing to conduct evidence syntheses. 

This guide will walk you through the major steps of a systematic review and point you to key resources including Covidence, a systematic review project management tool. For help with systematic reviews and other major literature review projects, please send us an email at  [email protected] .

Getting Help with Reviews

Organization such as the Institute of Medicine recommend that you consult a librarian when conducting a systematic review. Librarians at the University of Nevada, Reno can help you:

• Understand best practices for conducting systematic reviews and other evidence syntheses in your discipline
• Choose and formulate a research question
• Decide which review type (e.g., systematic, scoping, rapid, etc.) is the best fit for your project
• Determine what to include and where to register a systematic review protocol
• Select search terms and develop a search strategy
• Identify databases and platforms to search
• Find the full text of articles and other sources
• Become familiar with free citation management (e.g., EndNote, Zotero)
• Get access to you and help using Covidence, a systematic review project management tool

Doing a Systematic Review

• Plan - This is the project planning stage. You and your team will need to develop a good research question, determine the type of review you will conduct (systematic, scoping, rapid, etc.), and establish the inclusion and exclusion criteria (e.g., you're only going to look at studies that use a certain methodology). All of this information needs to be included in your protocol. You'll also need to ensure that the project is viable - has someone already done a systematic review on this topic? Do some searches and check the various protocol registries to find out. 
• Identify - Next, a comprehensive search of the literature is undertaken to ensure all studies that meet the predetermined criteria are identified. Each research question is different, so the number and types of databases you'll search - as well as other online publication venues - will vary. Some standards and guidelines specify that certain databases (e.g., MEDLINE, EMBASE) should be searched regardless. Your subject librarian can help you select appropriate databases to search and develop search strings for each of those databases.  
• Evaluate - In this step, retrieved articles are screened and sorted using the predetermined inclusion and exclusion criteria. The risk of bias for each included study is also assessed around this time. It's best if you import search results into a citation management tool (see below) to clean up the citations and remove any duplicates. You can then use a tool like Rayyan (see below) to screen the results. You should begin by screening titles and abstracts only, and then you'll examine the full text of any remaining articles. Each study should be reviewed by a minimum of two people on the project team. 
• Collect - Each included study is coded and the quantitative or qualitative data contained in these studies is then synthesized. You'll have to either find or develop a coding strategy or form that meets your needs. 
• Explain - The synthesized results are articulated and contextualized. What do the results mean? How have they answered your research question?
• Summarize - The final report provides a complete description of the methods and results in a clear, transparent fashion. 

Adapted from

Types of reviews, systematic review.

These types of studies employ a systematic method to analyze and synthesize the results of numerous studies. "Systematic" in this case means following a strict set of steps - as outlined by entities like PRISMA and the Institute of Medicine - so as to make the review more reproducible and less biased. Consistent, thorough documentation is also key. Reviews of this type are not meant to be conducted by an individual but rather a (small) team of researchers. Systematic reviews are widely used in the health sciences, often to find a generalized conclusion from multiple evidence-based studies. 

Meta-Analysis

A systematic method that uses statistics to analyze the data from numerous studies. The researchers combine the data from studies with similar data types and analyze them as a single, expanded dataset. Meta-analyses are a type of systematic review.

Scoping Review

A scoping review employs the systematic review methodology to explore a broader topic or question rather than a specific and answerable one, as is generally the case with a systematic review. Authors of these types of reviews seek to collect and categorize the existing literature so as to identify any gaps.

Rapid Review

Rapid reviews are systematic reviews conducted under a time constraint. Researchers make use of workarounds to complete the review quickly (e.g., only looking at English-language publications), which can lead to a less thorough and more biased review. 

Narrative Review

A traditional literature review that summarizes and synthesizes the findings of numerous original research articles. The purpose and scope of narrative literature reviews vary widely and do not follow a set protocol. Most literature reviews are narrative reviews. 

Umbrella Review

Umbrella reviews are, essentially, systematic reviews of systematic reviews. These compile evidence from multiple review studies into one usable document. 

Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal , vol. 26, no. 2, 2009, pp. 91-108. doi: 10.1111/j.1471-1842.2009.00848.x .

• Next: Project Planning >>

Literature Reviews: Systematic, Scoping, Integrative

Characteristics of review types, choosing a review type.

Steps in a Systematic/Scoping/Integrative Review

Confirming the Knowledge Gap

Standards and reporting guidelines.

• Creating a Search Strategy
• Limits and Inclusion Criteria
• Review Protocols
• Elements of a Systematic Review
• Review Tools and Applications

Additional Resources

• JBI Manual for Evidence Synthesis Process outlines for multiple types of evidence reviews. A great source to cite in your methods section.
• PRISMA Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Guidance for authors and peer reviewers on best practices in reporting for evidence reviews. Includes extensions for different types of reviews, including scoping reviews

Help us improve the LibGuide

Not sure which review type is right for your research question? Check out the links below for help choosing.

• What Review is Right for You? v2 14 page PDF survey to help you determine which review type might work best for you. Very thorough!
• Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. Munn, Z., Peters, M. D. J., Stern, C., Tufanaru, C., McArthur, A., & Aromataris, E. (2018). Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Medical Research Methodology, 18(1), 143. https://doi.org/10.1186/s12874-018-0611-x

Creating an effective search for a systematic review means walking a tightrope between comprehensiveness and managability. You want to try to include all of the studies that could possibly be relevant while simultaneously getting your search results down to a number of articles that you can realistically review. 

The Basic Process:

• Develop a research question.
• Consult with a librarian for help with steps 3-16.
• Search databases to see if a review has already been published on your topic. 
• Search protocol repositories to see if a review on your topic is planned.
• Select the type of review (systematic, scoping, integrative). This will require running some test searches to see if there is enough literature to merit a systematic review.
• Select databases.
• Select grey literature sources (if applicable). Read this article for helpful suggestions on systematically searching for grey literature.
• Formulate an initial search for one of your selected databases. For tips on searching, consult our Mastering Keyword Searching guide.
• Review results from initial search, scanning titles, abstracts, and subject headings to identify additional terms. You may also want to use the subject heading database you can find within each database.
• Run the search again. Continue to add relevant terms and adjust the scope of your question (which may require eliminating terms) until results are a reasonable size and predominantly relevant to your question.
• When you think your search is nearly final, gather 2-3 of your most relevant articles and test their reference lists against your search results. If your search contains a large majority of the relevant articles from those reference lists, your have your final search (remember no search is ever perfect, and you will nearly always add articles you find via reference lists, recommendations, etc. that did not appear in your search results). 
• Translate your search to your other databases. Generally your keywords will stay the same across databases, but you will most likely need to adjust your subject headings, because those can vary from database to database.
• Ask a librarian to peer review your search. Try the PRESS checklist . 
• Develop inclusion and exclusion criteria in preparation for reviewing articles (this step may come later for a scoping review)
• Write a protocol .
• Database name (be as specific as possible, including the full title, especially for databases that are offered in multiple formats, e.g. Ovid Medline) and dates of coverage.
• Search terms, including indicating which are subject headings and which are keywords plus any limitations to where the keywords were search if relevant.
• Database limits/filters applied to the results (e.g. publication year, language, etc.).
• Date of your search.
• Number of results.
• Begin title/abstract screening. Two reviewers for each item is best practice.
• Begin full-text review of the articles still remaining. Again, two reviewers for each item is best practice. 
• Conduct citation mining for the articles that make it through full-text review. That means looking at reference lists (backwards searching) and searching for articles that cite back to the article you have (forward searching). You might also consider setting aside all of the systematic and scoping reviews that came up with your search (generally those are excluded from your review) and mining their reference lists as well. Repeat the title/abstract screening and full-text reviews for the articles identified through citation mining.
• Check all articles that made it through the full-text review for retractions, and remove any articles that have been retracted. 
• If doing a systematic review, conduct a critical appraisal of included articles (aka Risk of Bias Assessment).
• Covidence. (2024). A practical guide to data extraction for intervention systematic reviews .
• Pollock et al. (2023). Recommendations for the extraction, analysis, and presentation of results in scoping reviews . JBI Evidence Synthesis, 21 (3), 520-532. 
• Prepare your manuscript (for information on writing each section of your manuscript, see our guide to Writing up Your Own Research ). 

Before beginning your review, you need to be sure that no other reviews with the same research question as yours already exist or are in progress. This is easily done by searching research databases and protocol registries.

Databases to Check

Protocol Registries

• PROSPERO PROSPERO accepts registrations for systematic reviews, rapid reviews and umbrella reviews. PROSPERO does not accept scoping reviews or literature scans. Sibling PROSPERO sites register systematic reviews of human studies and systematic reviews of animal studies.

It is a good idea to familiarize yourself with the standards and reporting guidelines for the type of review you are planning to do. Following the standards/guidelines as you plan and execute your review will help ensure that you minimize bias and maximize your chances of getting published.

Systematic Reviews

• PRISMA Statement The PRISMA statement is currently the standards and guidelines of choice for systematic reviews. At the link you will find the statement as well as explanations of each element, a checklist of elements, a PRISMA flow diagram template, and more.

• IOM Finding What Works in Healthcare: Standards for Systematic Reviews Standards from the National Academy of Medicine and National Academies Press. The free download link is all the way over on the right.

Scoping Reviews

• PRISMA-SCR Extension for Scoping Reviews A PRISMA statement, explanation and checklist specifically for scoping reviews.
• Updated methodological guidance for the conduct of scoping reviews While the PRISMA-SCR provides reporting guidelines, these guidelines from JBI are for how to actually plan and do your review. This is the explanation for updates made to the manual linked below. You can skip this article and go directly to the JBI manual if you prefer.

Integrative Reviews

• Whittemore, R., & Knafl, K. (2005). The integrative review: updated methodology. Journal of Advanced Nursing, 52 (5), 546–553. This article is the current standard for designing an integrative review. more... less... https://doi.org/10.1111/j.1365-2648.2005.03621.x
• Tavares de Souza, M., Dias da Silva, M., & de Carvalho, R. (2010). Integrative review: What is it? How to do it? Einstein, 8 (1). https://doi.org/10.1590/s1679-45082010rw1134
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• Last Updated: May 15, 2024 1:07 PM
• URL: https://libguides.massgeneral.org/reviews

Systematic Reviews: Scoping Reviews

• Systematic Review Defined
• Guides, Standards and Resources
• Data Extraction
• Risk of Bias
• WCM's Data Retention Policy & Systematic Reviews
• Scoping Reviews
• Narrative Reviews
• Covidence This link opens in a new window
• Collaborations 2022-present
• Collaborations 2012-2021

What is a Scoping Review?

Our Systematic Review Service can also assist you and your team with Scoping Reviews. 

A scoping review is a relatively new approach to evidence synthesis and differs from systematic reviews in its purpose and aims. The purpose of a scoping review is to provide an overview of the available research evidence without producing a summary answer to a guide clinical decision-making.

Scoping reviews are a form of knowledge synthesis, which incorporate a range of study designs to comprehensively summarize and synthesize evidence with the aim of informing practice, programs, and policy and providing direction to future research priorities.

The general purpose for conducting scoping reviews is to identify and map the available evidence.

Adapted from: Arksey H, O’Malley L. Scoping studies: towards a methodological framework. Int J Soc Res Methodol. 2005 Feb;8(1):19–32.

Sucharew H, Macaluso, M. Methods for Research Evidence Synthesis: The Scoping Review Approach. J. Hosp. Med 2019;7;416-418.

How is this different from a Systematic Review?

• Scoping reviews share a number of the same processes as systematic reviews, as they both use rigorous and transparent methods to comprehensively identify and analyze all the relevant literature pertaining to a research question.
• The key differences between the two review methods can be attributed to their differing purposes and aims. The purpose of a scoping review is to map the body of literature on a topic area . The purpose of a systematic review is to synthesize the best available research on a specific intervention . 
• Scoping reviews identify key characteristics or factors related to a concept. They do not produce statements to guide decision-making. 
• A scoping review seeks to present an overview of a potentially large and diverse body of literature pertaining to a broad topic . A systematic review attempts to collate empirical evidence from a relatively smaller number of studies pertaining to a focused research question. 
• Scoping reviews aim to provide a descriptive overview of the reviewed material without critically appraising individual studies or synthesizing evidence from different studies (no risk of bias or meta-analysis/statistical pooling is performed). In contrast, systematic reviews aim to provide a synthesis of evidence from studies assessed for risk of bias .

Adapted from: Pham MT, Rajić A, Greig JD, Sargeant JM, Papadopoulos A, McEwen SA. A scoping review of scoping reviews: advancing the approach and enhancing the consistency. Res Synth Methods. 2014 Dec;5(4):371–85.  

The PCC Question Development Framework

Because the aim of a scoping review differs from that of a systematic review, question development may not fit into the PICO (Patient/Intervention/Comparison/Outcome) framework . Therefore, PCC (Population/Concept/Context) may be a more useful framework.

Per JBI's Scoping Review Manual : "The 'PCC' mnemonic is recommended as a guide to construct a clear and meaningful title for a scoping review. The PCC mnemonic stands for the Population, Concept, and Context. There is no need for explicit outcomes, interventions or phenomena of interest to be stated for a scoping review; however elements of each of these may be implicit in the concept under examination."

When do I perform a Systematic Review? When do I perform a Scoping Review?

• When you have a specific clinical question that fits into the PICO framework or a hypothesis you are looking to test, you'll want to perform a systematic review. 
• If you are looking for a broad overview on a topic, with no hypothesis or specific clinical question, you'll want to perform a scoping review.  

Adapted from: Munn Z, Peters MDJ, Stern C, Tufanaru C, McArthur A, Aromataris E. Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Med Res Methodol. 2018 Nov 19;18(1):143.

How are both Systematic and Scoping Reviews different from Traditional Literature Reviews?

Systematic and scoping reviews aim to be comprehensive, transparent, reproducible, and unbiased – this is not typically the case with a traditional literature review. With clear and explicit methodology, the reader knows exactly how the authors of a study came to their conclusions, rather than relying on expert opinion or subjective selection that is usually found in a literature review. 

Additional Resources

• Peters MDJ, Marnie C, Tricco AC, Pollock D, Munn Z, Alexander L, McInerney P, Godfrey CM, Khalil H. Updated methodological guidance for the conduct of scoping reviews . JBI Evid Synth. 2020 Oct;18(10):2119-2126.
• Tricco AC, Lillie E, Zarin W, O’Brien KK, Colquhoun H, Levac D, et al. PRISMA Extension for Scoping Reviews (PRISMA-ScR): checklist and explanation . Ann Intern Med. 2018 Oct 2;169(7):467–73.
• Peters MDJ, Godfrey C, McInerney P, Munn Z, Tricco AC, Khalil, H. Chapter 11: Scoping Reviews (2020 version) . In: Aromataris E, Munn Z (Editors). JBI Manual for Evidence Synthesis, JBI, 2020.
• Munn Z, Peters MDJ, Stern C, Tufanaru C, McArthur A, Aromataris E. Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach . BMC Med Res Methodol. 2018 Nov 19;18(1):143.
• Arksey H, O’Malley L. Scoping studies: towards a methodological framework . Int J Soc Res Methodol. 2005 Feb;8(1):19–32.
• Pham MT, Rajić A, Greig JD, Sargeant JM, Papadopoulos A, McEwen SA. A scoping review of scoping reviews: advancing the approach and enhancing the consistency . Res Synth Methods. 2014 Dec;5(4):371–85.
• Colquhoun HL, Levac D, O’Brien KK, Straus S, Tricco AC, Perrier L, et al. Scoping reviews: time for clarity in definition, methods, and reporting . J Clin Epidemiol. 2014 Dec;67(12):1291–4.
• Peters MDJ, Godfrey CM, Khalil H, McInerney P, Parker D, Soares CB. Guidance for conducting systematic scoping reviews . Int J Evid Based Healthc. 2015 Sep;13(3):141–6.
• << Previous: WCM's Data Retention Policy & Systematic Reviews
• Next: Narrative Reviews >>
• Last Updated: May 2, 2024 10:36 AM
• URL: https://med.cornell.libguides.com/systematicreviews

Integrative Review

• Introduction
• Systematic vs. Scoping vs. Integrative
• Related Guides
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Systematic vs. Scoping vs. Integrative Review

• If you are wondering whether to perform a scoping review, integrative review, or systematic review, the following summaries can help you determine which review type is most appropriate for your research or clinical question. Grant and Booth (2009)  and Whittemore et al (2014)  describe additional review types that may better fit your research.
• Please note : The heading for each column in the table below links to Gumberg Library research guides.
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Systematic reviews and other evidence synthesis projects

• Types of Reviews
• Systematic Reviews
• 0. Plan your Review
• 1. Define the Question
• 2. Check for Recent Systematic Reviews and Protocols
• 3. Write and register your protocol
• Developing your Search Terms
• Database Search Tips and Filters
• Grey Literature
• Record and Report your Search Strategy
• Covidence This link opens in a new window
• 6. Appraise the Studies
• 7. Extract Data
• 8. Analyze / Synthesize Data
• 9. Write the Review
• Rapid Reviews

What is a Scoping Review?

Scoping review steps, scoping reviews vs. systematic reviews, the pcc framework, learning resources, guide design credit.

• Equity in Evidence Synthesis
• Automation, AI, and other upcoming review technologies
• Librarian Support

A scoping review is a broad overview of a general topic that maps a large and diverse body of literature to provide forms of evidence. 

Objectives of a Scoping Review

• To identify the types of available evidence in a given field
• To clarify key concepts/ definitions in the literature
• To examine how research is conducted on a certain topic or field
• To identify key characteristics or factors related to a concept
• As a precursor to a systematic review
• To identify and analyze knowledge gaps

Note: The full scoping review methodology is outside the scope of almost all class assignments or dissertation/thesis. If you are considering assigning one, please meet with a librarian about a modified version that will fit your course's needs and limits.

The following are the steps for the scoping review process:

• Determine subject for review and develop some general questions
• Highly recommended to develop a protocol after the first step!
• Use the PCC framework
• Conduct systematic searches
• Determine eligibility of papers from results with a screening process
• Data extraction of relevant information
• Document the evidence
• See also: the JBI scoping review YouTube playlist

Scoping reviews share a lot of the same methodology as systematic reviews, but there are some differences.

Scoping reviews answer different types of questions than systematic reviews. Arksey and O'Malley identified 4 reasons to conduct a scoping review:

• To examine the extent, range and nature of research activity
• To determine the value of undertaking a full systematic review
• To summarize and disseminate research findings
• To identify research gaps in the existing literature

Writing your protocol

The JBI Scoping Review chapter has guidance on writing your protocol. Also, the National Institutes of Health (NIH) Library has developed a Scoping Review Protocol Guidance template and informational document containing goals and requirements for the protocol plus helpful tips and examples.

Registering your protocol

There is not as centralized a location for registering scoping review protocols as there is for systematic reviews, but there are a few ways to do it. You can put it into an open science repository such as:

These have the added features of being a place where you can make any supplemental materials available, such as the full text of your searches, and the advantage of being fast since they don’t require the approval process of the journals below. They have the disadvantage of the protocol only being findable by people searching that repository.

There are also several journals that publish protocols:

• BMC Systematic Reviews  
• JMIR Research Protocols
• JBI Evidence Synthesis

These have the advantage of being included in several databases, but the disadvantage of having to go through the submission and approval process.

The PCC framework stand for the following and include these elements:

This framework can be used for mixed methods of qualitative and quantitative research.

By using this framework, it is also important to surface the varying including and excluding criteria to explicitly guide the scope of what is being investigated. This is helpful to document in your protocol to provide clarity about what information needs to be looked for in supporting your research question. 

• Systematic vs Scoping Review: What's the Difference? A short video from Carrie Price.
• Should I undertake a scoping review or a systematic review? A video from JBI.
• Scoping reviews: What they are and how you can do them on YouTube  or on Cochrane's website   Cochrane video training series.
• Pham MT, Rajić A, Greig JD, Sargeant JM, Papadopoulos A, McEwen SA. A scoping review of scoping reviews: advancing the approach and enhancing the consistency. Res Synth Methods. 2014 Dec;5(4):371-85. doi: 10.1002/jrsm.1123. Epub 2014 Jul 24. PMID: 26052958; PMCID: PMC4491356.
• Levac, Danielle, Heather Colquhoun, and Kelly K. O'Brien. "Scoping studies: advancing the methodology." Implementation Science 5.1 (2010): 1-9. https://doi.org/10.1186/1748-5908-5-69
• Scoping reviews: reinforcing and advancing the methodology and application . Micah D. J. Peters, Casey Marnie, Heather Colquhoun, Chantelle M. Garritty, Susanne Hempel, Tanya Horsley, Etienne V. Langlois, Erin Lillie, Kelly K. O’Brien, Ӧzge Tunçalp, Michael G. Wilson, Wasifa Zarin & Andrea C. Tricco. Systematic Reviews volume 10, Article number: 263 (2021)
• Khalil H, Peters M, Godfrey CM, McInerney P, Soares CB, Parker D. An Evidence-Based Approach to Scoping Reviews. Worldviews Evid Based Nurs. 2016 Apr;13(2):118-23. doi: 10.1111/wvn.12144 . Epub 2016 Jan 28. PMID: 26821833 .
• Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach ; by Zachary Munn, Micah D. J. Peters, Cindy Stern, Catalin Tufanaru, Alexa McArthur & Edoardo Aromataris. BMC Med Res Methodol 18, 143 (2018). https://doi.org/10.1186/s12874-018-0611-x
• Evidence maps - often based on a ScR: Miake-Lye IM, Hempel S, Shanman R, Shekelle PG. What is an evidence map? A systematic review of published evidence maps and their definitions, methods, and products . Syst Rev. 2016;5(1):28.

Reporting Guidelines

• PRISMA Extension for Scoping Reviews The PRISMA extension for scoping reviews, or PRISMA-ScR for short, contains 20 essential reporting items and 2 optional items to include when completing a scoping review.

Dev Wilder UW MLIS Candidate 2023

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• Last Updated: May 10, 2024 11:37 AM
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Literature Reviews

• Types of reviews
• Getting started

Types of reviews and examples

Choosing a review type.

• 1. Define your research question
• 2. Plan your search
• 3. Search the literature
• 4. Organize your results
• 5. Synthesize your findings
• 6. Write the review
• Artificial intelligence (AI) tools
• Thompson Writing Studio This link opens in a new window
• Need to write a systematic review? This link opens in a new window

Contact a Librarian

Ask a Librarian

• Meta-analysis
• Systematized

Definition:

"A term used to describe a conventional overview of the literature, particularly when contrasted with a systematic review (Booth et al., 2012, p. 265).

Characteristics:

• Provides examination of recent or current literature on a wide range of subjects
• Varying levels of completeness / comprehensiveness, non-standardized methodology
• May or may not include comprehensive searching, quality assessment or critical appraisal

Mitchell, L. E., & Zajchowski, C. A. (2022). The history of air quality in Utah: A narrative review.  Sustainability ,  14 (15), 9653.  doi.org/10.3390/su14159653

Booth, A., Papaioannou, D., & Sutton, A. (2012). Systematic approaches to a successful literature review. London: SAGE Publications Ltd.

"An assessment of what is already known about a policy or practice issue...using systematic review methods to search and critically appraise existing research" (Grant & Booth, 2009, p. 100).

• Assessment of what is already known about an issue
• Similar to a systematic review but within a time-constrained setting
• Typically employs methodological shortcuts, increasing risk of introducing bias, includes basic level of quality assessment
• Best suited for issues needing quick decisions and solutions (i.e., policy recommendations)

Learn more about the method:

Khangura, S., Konnyu, K., Cushman, R., Grimshaw, J., & Moher, D. (2012). Evidence summaries: the evolution of a rapid review approach.  Systematic reviews, 1 (1), 1-9.  https://doi.org/10.1186/2046-4053-1-10

Virginia Commonwealth University Libraries. (2021). Rapid Review Protocol .

Quarmby, S., Santos, G., & Mathias, M. (2019). Air quality strategies and technologies: A rapid review of the international evidence.  Sustainability, 11 (10), 2757.  https://doi.org/10.3390/su11102757

Grant, M.J. & Booth, A. (2009). A typology of reviews: an analysis of the 14 review types and associated methodologies.  Health Information & Libraries Journal , 26(2), 91-108. https://www.doi.org/10.1111/j.1471-1842.2009.00848.x

Developed and refined by the Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre), this review "map[s] out and categorize[s] existing literature on a particular topic, identifying gaps in research literature from which to commission further reviews and/or primary research" (Grant & Booth, 2009, p. 97).

Although mapping reviews are sometimes called scoping reviews, the key difference is that mapping reviews focus on a review question, rather than a topic

Mapping reviews are "best used where a clear target for a more focused evidence product has not yet been identified" (Booth, 2016, p. 14)

Mapping review searches are often quick and are intended to provide a broad overview

Mapping reviews can take different approaches in what types of literature is focused on in the search

Cooper I. D. (2016). What is a "mapping study?".  Journal of the Medical Library Association: JMLA ,  104 (1), 76–78. https://doi.org/10.3163/1536-5050.104.1.013

Miake-Lye, I. M., Hempel, S., Shanman, R., & Shekelle, P. G. (2016). What is an evidence map? A systematic review of published evidence maps and their definitions, methods, and products.  Systematic reviews, 5 (1), 1-21.  https://doi.org/10.1186/s13643-016-0204-x

Tainio, M., Andersen, Z. J., Nieuwenhuijsen, M. J., Hu, L., De Nazelle, A., An, R., ... & de Sá, T. H. (2021). Air pollution, physical activity and health: A mapping review of the evidence.  Environment international ,  147 , 105954.  https://doi.org/10.1016/j.envint.2020.105954

Booth, A. (2016). EVIDENT Guidance for Reviewing the Evidence: a compendium of methodological literature and websites . ResearchGate. https://doi.org/10.13140/RG.2.1.1562.9842 . 

Grant, M.J. & Booth, A. (2009). A typology of reviews: an analysis of the 14 review types and associated methodologies.  Health Information & Libraries Journal , 26(2), 91-108.  https://www.doi.org/10.1111/j.1471-1842.2009.00848.x

"A type of review that has as its primary objective the identification of the size and quality of research in a topic area in order to inform subsequent review" (Booth et al., 2012, p. 269).

• Main purpose is to map out and categorize existing literature, identify gaps in literature—great for informing policy-making
• Search comprehensiveness determined by time/scope constraints, could take longer than a systematic review
• No formal quality assessment or critical appraisal

Learn more about the methods :

Arksey, H., & O'Malley, L. (2005) Scoping studies: towards a methodological framework.  International Journal of Social Research Methodology ,  8 (1), 19-32.  https://doi.org/10.1080/1364557032000119616

Levac, D., Colquhoun, H., & O’Brien, K. K. (2010). Scoping studies: Advancing the methodology. Implementation Science: IS, 5, 69. https://doi.org/10.1186/1748-5908-5-69

Example : 

Rahman, A., Sarkar, A., Yadav, O. P., Achari, G., & Slobodnik, J. (2021). Potential human health risks due to environmental exposure to nano-and microplastics and knowledge gaps: A scoping review.  Science of the Total Environment, 757 , 143872.  https://doi.org/10.1016/j.scitotenv.2020.143872

A review that "[compiles] evidence from multiple...reviews into one accessible and usable document" (Grant & Booth, 2009, p. 103). While originally intended to be a compilation of Cochrane reviews, it now generally refers to any kind of evidence synthesis.

• Compiles evidence from multiple reviews into one document
• Often defines a broader question than is typical of a traditional systematic review

Choi, G. J., & Kang, H. (2022). The umbrella review: a useful strategy in the rain of evidence.  The Korean Journal of Pain ,  35 (2), 127–128.  https://doi.org/10.3344/kjp.2022.35.2.127

Aromataris, E., Fernandez, R., Godfrey, C. M., Holly, C., Khalil, H., & Tungpunkom, P. (2015). Summarizing systematic reviews: Methodological development, conduct and reporting of an umbrella review approach. International Journal of Evidence-Based Healthcare , 13(3), 132–140. https://doi.org/10.1097/XEB.0000000000000055

Rojas-Rueda, D., Morales-Zamora, E., Alsufyani, W. A., Herbst, C. H., Al Balawi, S. M., Alsukait, R., & Alomran, M. (2021). Environmental risk factors and health: An umbrella review of meta-analyses.  International Journal of Environmental Research and Public Dealth ,  18 (2), 704.  https://doi.org/10.3390/ijerph18020704

A meta-analysis is a "technique that statistically combines the results of quantitative studies to provide a more precise effect of the result" (Grant & Booth, 2009, p. 98).

• Statistical technique for combining results of quantitative studies to provide more precise effect of results
• Aims for exhaustive, comprehensive searching
• Quality assessment may determine inclusion/exclusion criteria
• May be conducted independently or as part of a systematic review

Berman, N. G., & Parker, R. A. (2002). Meta-analysis: Neither quick nor easy. BMC Medical Research Methodology , 2(1), 10. https://doi.org/10.1186/1471-2288-2-10

Hites R. A. (2004). Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations.  Environmental Science & Technology ,  38 (4), 945–956.  https://doi.org/10.1021/es035082g

A systematic review "seeks to systematically search for, appraise, and [synthesize] research evidence, often adhering to the guidelines on the conduct of a review" provided by discipline-specific organizations, such as the Cochrane Collaboration (Grant & Booth, 2009, p. 102).

• Aims to compile and synthesize all known knowledge on a given topic
• Adheres to strict guidelines, protocols, and frameworks
• Time-intensive and often takes months to a year or more to complete
• The most commonly referred to type of evidence synthesis. Sometimes confused as a blanket term for other types of reviews

Gascon, M., Triguero-Mas, M., Martínez, D., Dadvand, P., Forns, J., Plasència, A., & Nieuwenhuijsen, M. J. (2015). Mental health benefits of long-term exposure to residential green and blue spaces: a systematic review.  International Journal of Environmental Research and Public Health ,  12 (4), 4354–4379.  https://doi.org/10.3390/ijerph120404354

"Systematized reviews attempt to include one or more elements of the systematic review process while stopping short of claiming that the resultant output is a systematic review" (Grant & Booth, 2009, p. 102). When a systematic review approach is adapted to produce a more manageable scope, while still retaining the rigor of a systematic review such as risk of bias assessment and the use of a protocol, this is often referred to as a  structured review  (Huelin et al., 2015).

• Typically conducted by postgraduate or graduate students
• Often assigned by instructors to students who don't have the resources to conduct a full systematic review

Salvo, G., Lashewicz, B. M., Doyle-Baker, P. K., & McCormack, G. R. (2018). Neighbourhood built environment influences on physical activity among adults: A systematized review of qualitative evidence.  International Journal of Environmental Research and Public Health ,  15 (5), 897.  https://doi.org/10.3390/ijerph15050897

Huelin, R., Iheanacho, I., Payne, K., & Sandman, K. (2015). What’s in a name? Systematic and non-systematic literature reviews, and why the distinction matters. https://www.evidera.com/resource/whats-in-a-name-systematic-and-non-systematic-literature-reviews-and-why-the-distinction-matters/

• Review Decision Tree - Cornell University For more information, check out Cornell's review methodology decision tree.
• LitR-Ex.com - Eight literature review methodologies Learn more about 8 different review types (incl. Systematic Reviews and Scoping Reviews) with practical tips about strengths and weaknesses of different methods.
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• Last Updated: May 17, 2024 8:42 AM
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Basics of Systematic Reviews

• About Systematic Review

Types of Reviews

Literature review.

Collects key sources on a topic and discusses those sources in conversation with each other

• Standard for research articles in most disciplines
• Tells the reader what is known, or not known, about a particular issue, topic, or subject
• Demonstrates knowledge and understanding of a topic
• Establishes context or background for a case or argument
• Helps develop the author’s ideas and perspective

Rapid Review

Thorough methodology but with process limitations in place to expeditethe completion of a review.

• For questions that require timely answers
• 3-4 months vs. 12-24 months
• Limitations - scope, comprehensiveness bias, and quality of appraisal
• Discusses potential effects that the limited methods may have had on results

Scoping Review

Determine the scope or coverage of a body of literature on a given topic and give clear indication of the volume of literature and studies available as well as an overview of its focus.

• Identify types of available evidence in a given field
• Clarify key concepts/definitions in the literature
• Examine how research is conducted on a certain topic or field
• Identify key factors related to a concept
• Key difference is focus
• Identify and analyze knowledge gaps

Systematic Review

Attempts to identify, appraise, and summarize all empirical evidence that fits pre-specified eligibility criteria to answer a specific research question.

• clearly defined question with inclusion/exclusion criteria
• rigorous and systematic search of the literature
• thorough screening of results
• data extraction and management
• analysis and interpretation of results
• risk of bias assessment of included studies

Meta-Analysis

Used to systematically synthesize or merge the findings of single, independent studies, using statistical methods to calculate an overall or ‘absolute’ effect.

• Combines results from multiple empirical studies
• Requires systematic review first
• Use well recognized, systematic methods to account for differences in sample size, variability (heterogeneity) in study approach and findings (treatment effects)
• Test how sensitive their results are to their own systematic review protocol

For additional types of reviews please see these articles:

• Sutton, A., Clowes, M., Preston, L. and Booth, A. (2019), Meeting the review family: exploring review types and associated information retrieval requirements. Health Info Libr J, 36: 202-222. https://doi.org/10.1111/hir.12276
• Grant, M.J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26: 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x
• << Previous: About Systematic Review
• Next: Sources >>
• Last Updated: May 17, 2024 10:04 AM
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• Open access
• Published: 14 May 2024

Protocol for a scoping review study on learning plan use in undergraduate medical education

• Anna Romanova   ORCID: orcid.org/0000-0003-1118-1604 1 ,
• Claire Touchie 1 ,
• Sydney Ruller 2 ,
• Victoria Cole 3 &
• Susan Humphrey-Murto 4  

Systematic Reviews volume  13 , Article number:  131 ( 2024 ) Cite this article

79 Accesses

Metrics details

The current paradigm of competency-based medical education and learner-centredness requires learners to take an active role in their training. However, deliberate and planned continual assessment and performance improvement is hindered by the fragmented nature of many medical training programs. Attempts to bridge this continuity gap between supervision and feedback through learner handover have been controversial. Learning plans are an alternate educational tool that helps trainees identify their learning needs and facilitate longitudinal assessment by providing supervisors with a roadmap of their goals. Informed by self-regulated learning theory, learning plans may be the answer to track trainees’ progress along their learning trajectory. The purpose of this study is to summarise the literature regarding learning plan use specifically in undergraduate medical education and explore the student’s role in all stages of learning plan development and implementation.

Following Arksey and O’Malley’s framework, a scoping review will be conducted to explore the use of learning plans in undergraduate medical education. Literature searches will be conducted using multiple databases by a librarian with expertise in scoping reviews. Through an iterative process, inclusion and exclusion criteria will be developed and a data extraction form refined. Data will be analysed using quantitative and qualitative content analyses.

By summarising the literature on learning plan use in undergraduate medical education, this study aims to better understand how to support self-regulated learning in undergraduate medical education. The results from this project will inform future scholarly work in competency-based medical education at the undergraduate level and have implications for improving feedback and supporting learners at all levels of competence.

Scoping review registration:

Open Science Framework osf.io/wvzbx.

Peer Review reports

Competency-based medical education (CBME) has transformed the approach to medical education to focus on demonstration of acquired competencies rather than time-based completion of rotations [ 1 ]. As a result, undergraduate and graduate medical training programs worldwide have adopted outcomes-based assessments in the form of entrustable professional activities (EPAs) comprised of competencies to be met [ 2 ]. These assessments are completed longitudinally by multiple different evaluators to generate an overall impression of a learner’s competency.

In CBME, trainees will progress along their learning trajectory at individual speeds and some may excel while others struggle to achieve the required knowledge, skills or attitudes. Therefore, deliberate and planned continual assessment and performance improvement is required. However, due to the fragmented nature of many medical training programs where learners rotate through different rotations and work with many supervisors, longitudinal observation is similarly fragmented. This makes it difficult to determine where trainees are on their learning trajectories and can affect the quality of feedback provided to them, which is a known major influencer of academic achievement [ 3 ]. As a result, struggling learners may not be identified until late in their training and the growth of high-performing learners may be stifled [ 4 , 5 , 6 ].

Bridging this continuity gap between supervision and feedback through some form of learner handover or forward feeding has been debated since the 1970s and continues to this day [ 5 , 7 , 8 , 9 , 10 , 11 ]. The goal of learner handover is to improve trainee assessment and feedback by sharing their performance and learning needs between supervisors or across rotations. However, several concerns have been raised about this approach including that it could inappropriately bias subsequent assessments of the learner’s abilities [ 9 , 11 , 12 ]. A different approach to keeping track of trainees’ learning goals and progress along their learning trajectories is required. Learning plans (LPs) informed by self-regulated learning (SRL) theory may be the answer.

SRL has been defined as a cyclical process where learners actively control their thoughts, actions and motivation to achieve their goals [ 13 ]. Several models of SRL exist but all entail that the trainee is responsible for setting, planning, executing, monitoring and reflecting on their learning goals [ 13 ]. According to Zimmerman’s SRL model, this process occurs in three stages: forethought phase before an activity, performance phase during an activity and self-reflection phase after an activity [ 13 ]. Since each trainee leads their own learning process and has an individual trajectory towards competence, this theory relates well to the CBME paradigm which is grounded in learner-centredness [ 1 ]. However, we know that medical students and residents have difficulty identifying their own learning goals and therefore need guidance to effectively partake in SRL [ 14 , 15 , 16 , 17 ]. Motivation has also emerged as a key component of SRL, and numerous studies have explored factors that influence student engagement in learning [ 18 , 19 ]. In addition to meeting their basic psychological needs of autonomy, relatedness and competence, perceived learning relevance through meaningful learning activities has been shown to increase trainee engagement in their learning [ 19 ].

LPs are a well-known tool across many educational fields including CBME that can provide trainees with meaningful learning activities since they help them direct their own learning goals in a guided fashion [ 20 ]. Also known as personal learning plans, learning contracts, personal action plans, personal development plans, and learning goals, LPs are documents that outline the learner’s roadmap to achieve their learning goals. They require the learner to self-identify what they need to learn and why, how they are going to do it, how they will know when they are finished, define the timeframe for goal achievement and assess the impact of their learning [ 20 ]. In so doing, LPs give more autonomy to the learner and facilitate objective and targeted feedback from supervisors. This approach has been described as “most congruent with the assumptions we make about adults as learners” [ 21 ].

LP use has been explored across various clinical settings and at all levels of medical education; however, most of the experience lies in postgraduate medical education [ 22 ]. Medical students are a unique learner population with learning needs that appear to be very well suited for using LPs for two main reasons. First, their education is often divided between classroom and clinical settings. During clinical training, students need to be more independent in setting learning goals to meet desired competencies as their education is no longer outlined for them in a detailed fashion by the medical school curriculum [ 23 ]. SRL in the workplace is also different than in the classroom due to additional complexities of clinical care that can impact students’ ability to self-regulate their learning [ 24 ]. Second, although most medical trainees have difficulty with goal setting, medical students in particular need more guidance compared to residents due to their relative lack of experience upon which they can build within the SRL framework [ 25 ]. LPs can therefore provide much-needed structure to their learning but should be guided by an experienced tutor to be effective [ 15 , 24 ].

LPs fit well within the learner-centred educational framework of CBME by helping trainees identify their learning needs and facilitating longitudinal assessment by providing supervisors with a roadmap of their goals. In so doing, they can address current issues with learner handover and identification as well as remediation of struggling learners. Moreover, they have the potential to help trainees develop lifelong skills with respect to continuing professional development after graduation which is required by many medical licensing bodies.

An initial search of the JBI Database, Cochrane Database, MEDLINE (PubMed) and Google Scholar conducted in July–August 2022 revealed a paucity of research on LP use in undergraduate medical education (UGME). A related systematic review by van Houten–Schat et al. [ 24 ] on SRL in the clinical setting identified three interventions used by medical students and residents in SRL—coaching, LPs and supportive tools. However, only a couple of the included studies looked specifically at medical students’ use of LPs, so this remains an area in need of more exploration. A scoping review would provide an excellent starting point to map the body of literature on this topic.

The objective of this scoping review will therefore be to explore LP use in UGME. In doing so, it will address a gap in knowledge and help determine additional areas for research.

This study will follow Arksey and O’Malley’s [ 26 ] five-step framework for scoping review methodology. It will not include the optional sixth step which entails stakeholder consultation as relevant stakeholders will be intentionally included in the research team (a member of UGME leadership, a medical student and a first-year resident).

Step 1—Identifying the research question

The overarching purpose of this study is to “explore the use of LPs in UGME”. More specifically we seek to achieve the following:

Summarise the literature regarding the use of LPs in UGME (including context, students targeted, frameworks used)

Explore the role of the student in all stages of the LP development and implementation

Determine existing research gaps

Step 2—Identifying relevant studies

An experienced health sciences librarian (VC) will conduct all searches and develop the initial search strategy. The preliminary search strategy is shown in Appendix A (see Additional file 2). Articles will be included if they meet the following criteria [ 27 ]:

Participants

Medical students enrolled at a medical school at the undergraduate level.

Any use of LPs by medical students. LPs are defined as a document, usually presented in a table format, that outlines the learner’s roadmap to achieve their learning goals [ 20 ].

Any stage of UGME in any geographic setting.

Types of evidence sources

We will search existing published and unpublished (grey) literature. This may include research studies, reviews, or expert opinion pieces.

Search strategy

With the assistance of an experienced librarian (VC), a pilot search will be conducted to inform the final search strategy. A search will be conducted in the following electronic databases: MEDLINE, Embase, Education Source, APA PsycInfo and Web of Science. The search terms will be developed in consultation with the research team and librarian. The search strategy will proceed according to the JBI Manual for Evidence Synthesis three-step search strategy for reviews [ 27 ]. First, we will conduct a limited search in two appropriate online databases and analyse text words from the title, abstracts and index terms of relevant papers. Next, we will conduct a second search using all identified key words in all databases. Third, we will review reference lists of all included studies to identify further relevant studies to include in the review. We will also contact the authors of relevant papers for further information if required. This will be an iterative process as the research team becomes more familiar with the literature and will be guided by the librarian. Any modifications to the search strategy as it evolves will be described in the scoping review report. As a measure of rigour, the search strategy will be peer-reviewed by another librarian using the PRESS checklist [ 28 ]. No language or date limits will be applied.

Step 3—Study selection

The screening process will consist of a two-step approach: screening titles/abstracts and, if they meet inclusion criteria, this will be followed by a full-text review. All screening will be done by two members of the research team and any disagreements will be resolved by an independent third member of the team. Based on preliminary inclusion criteria, the whole research team will first pilot the screening process by reviewing a random sample of 25 titles/abstracts. The search strategy, eligibility criteria and study objectives will be refined in an iterative process. We anticipate several meetings as the topic is not well described in the literature. A flowchart of the review process will be generated. Any modifications to the study selection process will be described in the scoping review report. The papers will be excluded if a full text is not available. The search results will be managed using Covidence software.

Step 4—Charting the data

A preliminary data extraction tool is shown in Appendix B (see Additional file 3 ). Data will be extracted into Excel and will include demographic information and specific details about the population, concept, context, study methods and outcomes as they relate to the scoping review objectives. The whole research team will pilot the data extraction tool on ten articles selected for full-text review. Through an iterative process, the final data extraction form will be refined. Subsequently, two members of the team will independently extract data from all articles included for full-text review using this tool. Charting disagreements will be resolved by the principal and senior investigators. Google Translate will be used for any included articles that are not in the English language.

Step 5—Collating, summarising and reporting the results

Quantitative and qualitative analyses will be used to summarise the results. Quantitative analysis will capture descriptive statistics with details about the population, concept, context, study methods and outcomes being examined in this scoping review. Qualitative content analysis will enable interpretation of text data through the systematic classification process of coding and identifying themes and patterns [ 29 ]. Several team meetings will be held to review potential themes to ensure an accurate representation of the data. The PRISMA Extension for Scoping Reviews (PRISMA-ScR) will be used to guide the reporting of review findings [ 30 ]. Data will be presented in tables and/or diagrams as applicable. A descriptive summary will explain the presented results and how they relate to the scoping review objectives.

By summarising the literature on LP use in UGME, this study will contribute to a better understanding of how to support SRL amongst medical students. The results from this project will also inform future scholarly work in CBME at the undergraduate level and have implications for improving feedback as well as supporting learners at all levels of competence. In doing so, this study may have practical applications by informing learning plan incorporation into CBME-based curricula.

We do not anticipate any practical or operational issues at this time. We assembled a team with the necessary expertise and tools to complete this project.

Availability of data and materials

All data generated or analysed during this study will be included in the published scoping review article.

Abbreviations

• Competency-based medical education

Entrustable professional activity

• Learning plan
• Self-regulated learning
• Undergraduate medical education

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Acknowledgements

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This study will be supported through grants from the Department of Medicine at the Ottawa Hospital and the University of Ottawa. The funding bodies had no role in the study design and will not have any role in the collection, analysis and interpretation of data or writing of the manuscript.

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Anna Romanova & Claire Touchie

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Sydney Ruller

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Victoria Cole

The Ottawa Hospital – Riverside Campus, Ottawa, Canada

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AR designed and drafted the protocol. CT and SH contributed to the refinement of the research question, study methods and editing of the manuscript. VC designed the initial search strategy. All authors reviewed the manuscript for final approval. The review guarantors are CT and SH. The corresponding author is AR.

Authors’ information

AR is a clinician teacher and Assistant Professor with the Division of General Internal Medicine at the University of Ottawa. She is also the Associate Director for the internal medicine clerkship rotation at the General campus of the Ottawa Hospital.

CT is a Professor of Medicine with the Divisions of General Internal Medicine and Infectious Diseases at the University of Ottawa. She is also a member of the UGME Competence Committee at the University of Ottawa and an advisor for the development of a new school of medicine at Toronto Metropolitan University.

SH is an Associate Professor with the Department of Medicine at the University of Ottawa and holds a Tier 2 Research Chair in Medical Education. She is also the Interim Director for the Research Support Unit within the Department of Innovation in Medical Education at the University of Ottawa.

CT and SH have extensive experience with medical education research and have numerous publications in this field.

SR is a Research Assistant with the Division of General Internal Medicine at the Ottawa Hospital Research Institute.

VC is a Health Sciences Research Librarian at the University of Ottawa.

SR and VC have extensive experience in systematic and scoping reviews.

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Correspondence to Anna Romanova .

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Supplementary Information

Additional file 1. prisma-p 2015 checklist., 13643_2024_2553_moesm2_esm.docx.

Additional file 2: Appendix A. Preliminary search strategy [ 31 ].

Additional file 3: Appendix B. Preliminary data extraction tool.

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Romanova, A., Touchie, C., Ruller, S. et al. Protocol for a scoping review study on learning plan use in undergraduate medical education. Syst Rev 13 , 131 (2024). https://doi.org/10.1186/s13643-024-02553-w

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Research Article

Management of childbearing with hypermobile Ehlers-Danlos syndrome and hypermobility spectrum disorders: A scoping review and expert co-creation of evidence-based clinical guidelines

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliations Research Centre for Healthcare and Communities, Coventry University, Coventry, United Kingdom, The University of Notre Dame, Notre Dame, Australia

Roles Conceptualization, Data curation, Formal analysis, Investigation, Writing – review & editing

Affiliation Department of Connective Tissue, Nova Combian Research Institute, New York, New York, United States of America

Roles Data curation, Formal analysis, Investigation, Writing – review & editing

Affiliation The Ehlers Danlos Society’s International Consortium, New York, New York, United States of America

Affiliation Main Line Health- Bryn Mawr Rehab, King of Prussia, Pennsylvania, United States of America

Affiliation Department of Clinical Genetics, Erasmus Medical Centre, Rotterdam, The Netherlands

Roles Data curation, Formal analysis, Writing – original draft, Writing – review & editing

Affiliation The Ehlers-Danlos Society, The Ehlers-Danlos Society – Europe, London, United Kingdom

Affiliation Harris Whole Health, Fairfax, Virginia, United States of America

Affiliation Lehigh Valley Health Network, Palmer, Pennsylvania, United States of America

Affiliation The International Consortium on the Ehlers-Danlos syndromes and Hypermobility Spectrum Disorders, The Herds Nerd, Baltimore, Maryland, United States of America

Roles Data curation, Formal analysis, Investigation, Methodology, Validation, Writing – review & editing

Affiliation Integrative Systemic Medicine Center, Boulogne-Billancourt and Strasbourg University Hospital, Strasbourg, France

Affiliation GoodHope EDS Program, Toronto General Hospital, Toronto, Ontario, Canada

Affiliation Registered Dietitian Nutritionist, Ridgewood, New Jersey, United States of America

Roles Data curation, Formal analysis, Investigation, Validation, Writing – review & editing

Affiliation Women and Infants Hospital, An Affiliate of Warren Alpert Medical School at Brown University in Providence, Providence, Rhode Island, United States of America

Affiliation Lorna Ryan Health, London, United Kingdom

Roles Conceptualization, Data curation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing

Affiliation Harvey Institute for Human Genetics, Greater Baltimore Medical Center, Baltimore, Maryland, United States of America

• Sally Pezaro, 
• Isabelle Brock, 
• Maggie Buckley, 
• Sarahann Callaway, 
• Serwet Demirdas, 
• Alan Hakim, 
• Cheryl Harris, 
• Carole High Gross, 
• Megan Karanfil, 

• Published: May 15, 2024
• https://doi.org/10.1371/journal.pone.0302401
• Peer Review
• Reader Comments

To co-create expert guidelines for the management of pregnancy, birth, and postpartum recovery in the context of hypermobile Ehlers-Danlos syndrome (hEDS) and hypermobility spectrum disorders (HSD).

Scoping Review and Expert Co-creation.

United Kingdom, United States of America, Canada, France, Sweden, Luxembourg, Germany, Italy, and the Netherlands.

Co-creators (n = 15) included expertise from patients and clinicians from the International Consortium on the Ehlers-Danlos syndromes and Hypermobility Spectrum Disorders, facilitated by the Ehlers-Danlos Society.

A scoping review using Embase, Medline, the Cochrane Central Register of Controlled Trials and CINHAL was conducted from May 2022 to September 2023. Articles were included if they reported primary research findings in relation to childbearing with hEDS/HSD, including case reports. No language limitations were placed on our search, and our team had the ability to translate and screen articles retrieved in English, French, Spanish, Italian, Russian, Swedish, Norwegian, Dutch, Danish, German, and Portuguese. The Mixed Methods Appraisal Tool was used to assess bias and quality appraise articles selected. The co-creation of guidelines was based on descriptive evidence synthesis along with practical and clinical experience supported by patient and public involvement activities.

Primary research studies (n = 14) and case studies (n = 21) including a total of 1,260,317 participants informed the co-creation of guidelines in four overarching categories: 1) Preconceptual: conception and screening, 2) Antenatal: risk assessment, management of miscarriage and termination of pregnancy, gastrointestinal issues and mobility, 3) Intrapartum: risk assessment, birth choices (mode of birth and intended place of birth), mobility in labor and anesthesia, and 4) Postpartum: wound healing, pelvic health, care of the newborn and infant feeding. Guidelines were also included in relation to pain management, mental health, nutrition and the common co-morbidities of postural orthostatic tachycardia syndrome, other forms of dysautonomia, and mast cell diseases.

Conclusions

There is limited high quality evidence available. Individualized strategies are proposed for the management of childbearing people with hEDS/HSD throughout pregnancy, birth, and the postpartum period. A multidisciplinary approach is advised to address frequently seen issues in this population such as tissue fragility, joint hypermobility, and pain, as well as common comorbidities, including dysautonomia and mast cell diseases.

Citation: Pezaro S, Brock I, Buckley M, Callaway S, Demirdas S, Hakim A, et al. (2024) Management of childbearing with hypermobile Ehlers-Danlos syndrome and hypermobility spectrum disorders: A scoping review and expert co-creation of evidence-based clinical guidelines. PLoS ONE 19(5): e0302401. https://doi.org/10.1371/journal.pone.0302401

Editor: Martin E. Matsumura, Geisinger Health System, UNITED STATES

Received: January 11, 2024; Accepted: April 2, 2024; Published: May 15, 2024

Copyright: © 2024 Pezaro et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting information files.

Funding: The author(s) received no specific funding for this work.

Competing interests: SP reports receiving honorariums from the Ehlers-Danlos Society. AH reports receiving honorariums from the Ehlers-Danlos Society. NB reports receiving honorariums from the Ehlers-Danlos Society. Other authors report no conflict of interest.

Introduction

The Ehlers-Danlos syndromes (EDS) are a group of underdiagnosed, heritable connective tissue disorders characterized by generalized joint hypermobility (GJH), skin hyperextensibility and tissue fragility. Thirteen types of EDS were identified by the International Consortium on the Ehlers-Danlos Syndromes in 2017 [ 1 ], and a fourteenth subtype has since been identified [ 2 ]. Hypermobile EDS (hEDS) is the most common type of EDS, mainly symptomatic in people assigned female at birth [ 3 , 4 ]. Updated diagnostic criteria for hEDS released in 2017 narrowly define hEDS based on the presence of GJH, multiple features of underlying connective tissue weakness, with or without confirmed family history of the same diagnosis [ 1 ]. Those presenting with GJH, musculoskeletal complications and pain with or without associated comorbidities, who do not fulfill criteria of hEDS may fall under the diagnostic category of hypermobility spectrum disorders (HSD), for which the same management approaches will apply [ 5 , 6 ]. Thus hEDS/HSD are referred to together throughout this article, though we recognize that more will be diagnosed with HSD than hEDS. hEDS/HSD is likely underdiagnosed overall but recent estimations suggest that the combined prevalence of hEDS and HSD in the order of 1 in 600 to 1 in 900 [ 4 ], with many pregnancies affected [ 7 ]. Separate prevalence estimates for hEDS and HSD are not currently available. Patients with hEDS/HSD present with multisystem signs, symptoms, and comorbidities the most common of which are outlined in Table 1 , adapted from Hamonet and colleagues with permission [ 8 ].

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https://doi.org/10.1371/journal.pone.0302401.t001

Regarding frequencies presented in Table 1 , the control group had symptoms at <10% frequency, with the following exceptions: sleeping problems (26%), upper respiratory infections (23%), bloating or distension caused by gas (19%), gastroesophageal reflux (13%), and meno/metrorrhagia (11%).

Prevalence of obstetric, pelvic and reproductive system issues reported by those childbearing with hEDS/HSD are significantly greater than in the general childbearing population [ 9 , 10 ]. Symptoms can be debilitating; they may either be exacerbated or improve during pregnancy and birth, when hormonal levels are elevated [ 7 , 11 – 13 ]. Still, there is scarce literature related to perinatal care in the context of hEDS/HSD, leading to potential misconceptions and a lack of knowledge in some health care professionals [ 7 , 14 ]. Discussions with patient groups and members of the International Consortium on the Ehlers-Danlos syndromes and Hypermobility Spectrum Disorders established the importance of and need to have international expert guidelines drawing from existing evidence and expert opinion to provide guidance to care providers and persons with these conditions in childbearing. Moreover, evidence-based guidelines have been most commonly requested by both perinatal professionals and those childbearing with hEDS/HSD in a large international survey investigating perinatal staff’s knowledge and confidence in supporting people with hEDS/HSD, and people with hEDS/HSD’s experiences of perinatal care [ 14 ].

Considering the above, the overarching aim of this research was to co-create international evidence-based expert guidelines on the management of pregnancy, birth, and post-natal recovery in the context of hEDS/HSD. A scoping review was conducted to inform the co-creation of these guidelines and answer the following question: What is known from the literature about pregnancy, birth, and post-natal recovery in people with hEDS/HSD?

Scoping reviews differ from systematic reviews and lend themselves to scoping a body of literature while utilising the experience and expertise of their authors [ 15 ]. They are also complementary to co-creating guidelines and guidelines such as these [ 16 ] and are recommended to addresses several questions from a diverse body of literature pertaining to a broad topic. As such, a scoping review was considered the most rigorous approach to evaluate the evidence and inform these guidelines, rather than a systematic review, which is methodologically suited to address only one question. Our scoping review followed a preferred framework [ 17 ], consisting of the following steps: (1) identifying the research question(s), (2) identifying relevant studies, (3) study selection, (4) charting the data, (5) collating, summarising, and reporting the results, and (6) optional consultation exercises. We also included patient representatives and ensured stakeholder engagement throughout to enhance the rigor of our scoping approach [ 18 ]. This also met our objective with regards to using the findings of a scoping review to inform the co-creation of evidence-based guidelines in this context.

This research was undertaken using evidence-based approaches [ 19 ]. Alongside a scoping review, the three Co’s framework of ‘Co-define’ (examining problems and positive aspects), ‘Co-design’ (prioritising problems and designing solutions), ‘Co-refine’ (co-produce and refine together) was used to co-create the guidance presented [ 20 ]. Such co-creation is underpinned by participatory action research [ 21 – 23 ] and design thinking [ 24 , 25 ]. In person consensus meetings along with Patient and Public Involvement (PPI) activities involving wider patient and public groups and convened by the Ehlers-Danlos Society were also undertaken in finalizing the guidelines presented.

Co-creator recruitment began after ethical approval was granted via the lead author’s University in March 2022 (Project P135062). Our sampling strategy was purposive. Members of the International Consortium on the Ehlers-Danlos syndromes and Hypermobility Spectrum Disorders ( www.ehlers-danlos.com/international-consortium ), including those with lived experience of both hEDS/HSD and childbearing, along with clinicians and academics were sent participant information via email and were invited to participate.

Once informed consent was secured, each co-creator was given access to the project’s co-creation space online and invited to visit the ‘co-creating welfare’ project website ( http://ccw.southdenmark.eu/ ) to become familiar with the principles of co-creation. Those who gave their consent to participate were invited to engage in a series of online co-creation workshops hosted by the Ehlers-Danlos Society and led by the principal author.

During the first co-creation workshop, activities focused on ‘co-defining’ what the issues, problems, and positive aspects of perinatal care in this context are. Thereafter, co-creators were invited to prioritise the problems identified, find solutions, and ‘co-design’ expert guidance together in real time. These were then co-produced and refined together. Both during and outside of bi-weekly ‘co-refining’ workshops, co-creators were invited to ‘co-refine’ guidelines via an iterative succession of discussions and annotated co-refinements.

Co-creation began in March 2022 and concluded in November 2023 following a face-to-face consensus meeting held in Arizona (August 2022), and public and patient involvement activities held in Rome (September 2022) hosted by the Ehlers-Danlos Society. During 2023, four further co-refining workshops were hosted to discuss residual deviating views and ideas until unanimity was reached. In line with our evidence-based approach [ 19 ], co-creation activities were supported by our scoping review, which was last updated in September 2023. Expert co-creators consulted the findings of each article included and used these, along with their practical knowledge and/or experiences to support and inform the co-created guidelines.

The search strategy for our scoping review is outlined in Table 2 and was formulated in partnership with librarians at the Erasmus MC Medical Library in Rotterdam in the Netherlands, inclusive of previous nomenclature. The PRISMA extension for scoping reviews (PRISMA-ScR) was used to guide reporting (See checklist in S1 File ).

https://doi.org/10.1371/journal.pone.0302401.t002

Screening of the articles was led by two members of the team (SP and ILR) who engaged all co-creators in decision making during bi-weekly meetings. Final articles were included to inform the guidelines if they reported primary research findings in relation to childbearing with hEDS/HSD. Case reports were also included to inform the guidelines presented. No limits were placed with regards to the language of articles to be screened, and our team had the ability to translate and screen articles retrieved in the following languages: English, French, Spanish, Italian, Russian, Swedish, Norwegian, Dutch, Danish, German, and Portuguese. Articles were excluded if they did not relate to childbearing in the context of hEDS/HSD. Alongside the inclusion of newly published peer reviewed articles shared via professional networks, the reference lists of identified articles and literature reviews were also screened for additional relevant citations. Reviews of the literature were excluded if they did not also feature a clinical case study. Authors of all selected articles were invited to offer any further available evidence for inclusion. To further enhance the rigor of our approach, primary research articles (excluding case studies) which met inclusion criteria were then quality appraised using the Mixed Methods Appraisal Tool (MMAT), which enables researchers to simultaneously evaluate the validity and reliability of both quantitative and qualitative empirical studies [ 26 ]. Quality scores range from * if one criterion is met to ***** if all five criteria are met [ 27 ]. Final appraisal scores were proposed in consultation by 3 members of the team (ILR, SD and SP), and then agreed by the wider co-creation team.

Co-creators considered the identified evidence and contextualized it alongside the co-production of guidelines while engaging the principles of the WHO-INTEGRATE evidence to decision framework [ 28 ]. In line with best practice and where evidence was lacking [ 19 ], co-creators formulated guidelines based on practical and clinical experience, and with input from those with lived experiences. Once guidelines were finalized, external members of the International Consortium with relevant subject expertise distinct from those within the co-creation team were invited to assess the final guidelines for clarity and relevance.

This research occurred in a context where minoritized Black and other ethnic communities, the Lesbian, Gay, Bisexual, Transgender, Queer and/or Questioning, Intersex, Asexual, Two-Spirit (LGTBQIA2S+) communities and those with low socioeconomic status face challenges and experience discrimination in healthcare every day [ 29 ]. Consequently, gender-inclusive and person-first language was used throughout reporting. All co-creators were unanimous in approving the finalized guidelines reported here.

Patient and public involvement activities

Patient and stakeholder engagement in guideline development is internationally advocated [ 30 ]. We report the Patient and Public Involvement (PPI) activities conducted in line with the Guidance for Reporting Involvement of Patients and the Public (GRIPP2) short form checklist [ 31 ]. To reduce the potential for bias, prior relationships with those engaging in PPI activities and the co-creation team were minimal, and activities remained congruent with best practice [ 30 ].

The aim of PPI in this study was to involve members of the public and those with lived experience of hEDS/HSD and childbearing in the co-creation of international expert guidelines for the management of pregnancy, birth, and post-natal recovery in the context of hEDS/HSD. We were also keen to co-author and disseminate this publication with those who have had experience of childbearing with hEDS/HSD.

Patient representatives were involved in this project from its conception, both as co-creators, authors, and consultants with lived experience of hEDS/HSD and/or childbirth. All patients and public attending conferences hosted by the Ehlers-Danlos Society in both Arizona (August 2022) and Rome (September 2022) were invited to comment upon and shape guidelines in partnership with the co-creation team in person. Further comments were also solicited via the Ehlers-Danlos Society’s Global Affiliation Program newsletter, and via a separate EDS affiliate focus group facilitated online by MB including 12 participants representing USA, Canada, Sweden, Luxembourg, and Germany. All comments resulting from these activities were collated together and shared with the co-creation team. They were then examined collectively to identify common topics, ideas, and patterns of meaning which were then grouped into themes.

Themes related to ‘key topics’ for inclusion in the guidelines and related to the management of miscarriage and termination of pregnancy, comorbidities, causal relationships, anesthesia, incontinence, and risk assessments along with the management of symptoms such as enhanced joint laxity and pain. Those who engaged in PPI requested guidelines from the co-creation team with regards to the preconceptual, antenatal, intrapartum, and postpartum periods.

Discussion and conclusions.

PPI influenced this study substantially overall. A distinctly positive aspect of engaging in PPI from the start meant that we could stay focussed on what mattered most and communicate to professionals using the voices of those with lived experience. Nevertheless, it was challenging to balance the knowledge, voices, and concerns of experts with lived experience and practicing clinicians.

Reflections.

Due to previous negative experiences with clinicians in healthcare, some engaged with PPI activities were doubtful as to the ability of clinicians to use their initiative or provide basic, competent, and compassionate care, and thus requested that guidelines included basic principles of healthcare practice. This was frustrating to clinical professionals, who expressed fears that clinicians would disengage from guidelines which repeated their basic training. The rebuilding of trust between clinicians and those with lived experience in this area may remove this as a barrier to future PPI activities.

A total of 15 co-creators joined in meeting the aim of this research from the United Kingdom, United States of America, Canada, France, and the Netherlands. Co-creators represented a variety of professions including midwifery, obstetrics, maternal fetal medicine, rheumatology, registered dietitians, and nutritionists, physical therapy, clinical geneticists, nursing, clinical research, and pain management. Co-creators also included patient advocates with lived experience of both hEDS/HSD and childbearing. All co-creators joined in authoring the final report and guidelines, and thus are listed as co-authors to this article.

Fig 1 outlines how the final articles (n = 35) resulting from our literature searches were identified for inclusion following the removal of duplicates.

https://doi.org/10.1371/journal.pone.0302401.g001

The final articles which met our inclusion criteria consisted of primary research studies (n = 14) and case studies (n = 21). They included a total of 1,260,317 participants. Our collation and summarising of results are reported in Table 3 , which presents article details, findings, and quality appraisal scores.

https://doi.org/10.1371/journal.pone.0302401.t003

Final expert guidelines were broadly grouped into the following categories presented in Table 4 : Preconceptual (conception and screening), Antenatal (risk assessment, management of miscarriage and termination of pregnancy and mobility), Intrapartum (risk assessment, birth choices, mode of birth/intended place of birth, mobility in labour and anaesthesia), and Postpartum (wound healing, pelvic health, care of the newborn and infant feeding). Our supplement also outlines guidance in relation to physical therapy (see table in S2 File ). These are intended to act as guides rather than policy in the understanding that professionals take an individualized approach to care.

https://doi.org/10.1371/journal.pone.0302401.t004

This article presents an international consensus of expert guidelines in the management of childbearing with hEDS/HSD brought about using systematic and co-creation approaches along with a variety of PPI activities. While we have built upon previous care considerations [ 11 – 13 ], these guidelines represent the first of their kind from an international multidisciplinary collaboration, including patient perspectives. In our experts’ view, many of the guidelines made can be applicable in other subtypes of EDS (except vascular EDS), though each type should be considered individually via future research. Practitioners may also consider these expert guidelines for those with generalized HSD, as underlying care principles will be largely the same. Moreover, as JHS is indistinguishable from hEDS/HSD and considered likely allelic, this guideline should also apply to those diagnostically labelled as having JHS. We also offer strategies in relation to managing the comorbidities associated with hEDS/HSD, although we recognize that further research is required in these areas, and more detailed expert consensus’ remains warranted [ 73 , 74 , 123 ].

Guidelines were co-created into the following categories: Preconceptual (conception and screening), Antenatal (risk assessment, management of miscarriage and termination of pregnancy and mobility), Intrapartum (risk assessment, birth choices, mode of birth/intended place of birth, mobility in labor and anesthesia), and Postpartum (wound healing, pelvic health, care of the newborn and infant feeding). Our use of the wider literature in co-creation adds to earlier syntheses and understandings in this area [ 124 , 125 ]. Yet further research is required with regards to obstetric outcomes dependent upon the pregnant person’s and the unborn’ EDS status, particularly where outcomes in relation to specific types of EDS are not reported separately [ 82 , 126 ].

Due to their inextricable links, PPI activities and co-creators also directed us to provide expert guidelines in relation to some of the comorbidities of hEDS/HSD such as mast cell diseases and spinal instability [ 127 ]. Equally, these guidelines evolved to encompass dysautonomia, orthostatic intolerance with or without orthostatic hypotension and POTS, of which between 70% to ≥80% of those with hEDS/HSD may also experience symptoms related to childbearing [ 127 ]. Guidelines were also included in relation to pain management, mental health, nutrition, supplementation, allergies with immune responses, and overall wellbeing. Further resources and citations are also provided and should be referred to, particularly in relation to paediatrics [ 116 ].

In the assessment of risk in planning both the mode and place of birth, the anticipation of increased blood loss will be key in all cases. Individuals with hEDS/HSD typically have fragile capillaries and tissue, predisposing them to bruising and hematomas. In addition, some will have an abnormal interaction between Von Willebrand factor, platelets, and collagen resulting in suboptimal blood clotting which in turn can lead to heavier and prolonged bleeding [ 128 ]. During pregnancy, increased mucosal fragility can result in spontaneous bleeding (e.g., epistaxis and gingival). There may similarly be increased bleeding during childbirth [ 10 , 34 , 40 , 41 ]. Yet some large retrospective studies have found no increased risk for bleeding in such cases [ 35 , 36 ]. Nevertheless, alongside other more well-known treatments, we have been able to endorse a wider variety of medicines such as Desmopressin and Tranexamic Acid to control bleeding where applicable [ 99 , 100 ]. Due to the potential concern for precipitous birth in this population [ 7 , 10 ], it may be prudent to plan for births in a community setting with attention to distance to any birthing facilities.

It is useful to consider that the extensibility of all bodily tissues in those childbearing with hEDS/HSD may be greater than in the general childbearing population. During pregnancy, the entire body must be considered since pregnancy hormones such as relaxin influence the body systemically [ 128 ]. Those with hEDS/HSD can also present with a lower health related quality of life and greater psychological distress than those in the general population [ 118 ], which may be exacerbated by childbearing [ 10 ]. Some patients experience a relief in symptoms, particularly dysautonomia and pain. Due to the multifaceted nature of hEDS/HSD, a biopsychosocial approach may be most appropriate in all cases, whereby symptoms such as depression and anxiety are always assessed concurrently with physical symptoms and treated accordingly. In this task, a suite of co-created tools to help perinatal staff support people childbearing with hEDS/HSD may usefully be employed [ 14 ].

As connective tissues behave differently for those birthing with hEDS/HSD, it may be useful to investigate outcomes relating to alternate forms of analgesia (e.g., waterbirth) in these populations. Moreover, it is possible that some features of childbearing considered ‘typical’ may actually be associated with hEDS/HSD (e.g., precipitous birth), corresponding with joint hypermobility, skin hyperextensibility and other anomalies of connective tissue [ 10 ]. Future research activities could explore these potential links and avoid conflation between the various subtypes of EDS.

Using systematic and co-creation approaches along with a variety of PPI activities, this research is the first of its kind to offer consensus guidelines from an international and multidisciplinary group of experts in the field of childbearing with hEDS/HSD. Limitations include a lack of relevant, larger, longitudinal, and high-quality studies in this field. Those with hEDS/HSD may not have been diagnosed until after their childbearing experience, thus limiting clinical expertise in this area. Further research is required to compare outcomes of interventions designed to address all conditions more prevalent in this childbearing population (e.g., PGP) [ 128 ].

Due to conflicting findings and limited research in this area, the guidelines presented have also been guided by patient preference, clinical expertise, practicalities and known biological mechanisms. Inevitably, as evidence-based practitioners, some co-creators have also referenced other published evidence, for example in cases where we have made evidence-based guidelines for the use of complementary and alternative medicines such as acupuncture [ 69 ], though the usual contraindications associated with pregnancy still apply [ 129 ]. Furthermore, many research findings and guidelines published previously have been made for all EDS types, rather than for individuals with hEDS/HSD specifically. Thus, we have had to review and modify these in light of the wider evidence and expertise within the co-creation team. The quality of some evidence such as clinical case studies was low. Moreover, our scoping review is inherently limited as its focus was to provide breadth rather than depth of information. Many existing guidelines for pregnancy in general populations (e.g., in relation to exercise and pelvic girdle pain) remained relevant and considered equally beneficial with modification(39). Yet in other areas such as cervical insufficiency and preterm labor, further research will be required for more comprehensive guidelines.

A key challenge in conducting this research is that the inheritance of hEDS/HSD has yet to be determined, unlike the other types of EDS. Also, multiple family members may have hEDS/HSD, with significant variability in findings and symptoms among them. Whole exome sequencing has recently identified several genes of interest [ 65 ], but at this time there is no genetic testing available. Genetic factors may also play a role where incidence of multiple miscarriages of pregnancy (≥3 with the same partner) in this population is higher(30). Limitations in the literature include the fact that diagnoses of hEDS/HSD are often self-reported, and studies frequently report on all subtypes of EDS as a whole, where some of the rarer types (e.g., vascular) would likely bring increased complications. As hEDS/HSD does represent the vast majority of cases, it is likely representative of the complications reported. Yet even a minority of complications included from one of the rarer types of EDS in an amalgamated cohort study would skews results and thus, the interpretation of risk. Future research could usefully embark upon prospective studies which explore each subtype distinctly. Moreover, despite the risks and issues discussed in the guidelines presented here, it remains important not to over medicalize pregnancy, as many pregnancies in cases of hEDS/HSD are decidedly unremarkable.

The co-creation of evidence-based guidelines in the management of childbearing in cases of hEDS/HSD is justified given the lack of knowledge and awareness demonstrated by healthcare professionals and the profound impacts hEDS/HSD can have upon childbearing populations. Evidence in this area was found to be sparse and somewhat contradictory. Nevertheless, the expert guidelines established here by clinical, academic, and patient experts provide an evidence-informed basis for how care and outcomes may be improved for this childbearing population. In the spirit of evidence-based practice, such guidance could usefully evolve alongside future research in this field.

Other information

SP reports receiving honorariums from the Ehlers-Danlos Society. AH reports receiving honorariums from the Ehlers-Danlos Society. NB reports receiving honorariums from the Ehlers-Danlos Society. Other authors report no conflict of interest. All data extracted has been included in this report.

Supporting information

S1 file. prisma-scr..

PRISMA extension checklist for Scoping Reviews.

https://doi.org/10.1371/journal.pone.0302401.s001

S2 File. Supporting information.

Guidelines for physical therapy.

https://doi.org/10.1371/journal.pone.0302401.s002

Acknowledgments

The authors wish to thank Dr Maarten (M.F.M.) Engel from the Erasmus MC Medical Library for their support in developing and updating the search strategies. We would also like to thank the experts we consulted throughout, and the Ehlers Danlos Society.

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Centralized exchanges vs. decentralized exchanges in cryptocurrency markets: A systematic literature review

• Research Paper
• Open access
• Published: 18 May 2024
• Volume 34 , article number  33 , ( 2024 )

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• Sascha Hägele   ORCID: orcid.org/0009-0000-3224-7508 1  

Research on cryptocurrency exchanges, consisting of both centralized exchanges (CEXs) and decentralized exchanges (DEXs), has seen a significant increase in contributions in recent years, driven by growing interest in the conceptual design of cryptocurrency markets. Through a comprehensive review of literature published between January 2019 and September 2023, I identify and analyze different dimensions of the ongoing CEX vs. DEX debate. While DEXs emphasize decentralization, user control, and resistance to censorship, CEXs offer higher liquidity, advanced trading features, and a more established track record. Regulatory challenges, such as Know Your Customer (KYC) and Anti-Money Laundering (AML) compliance, also feature prominently in the literature and influence the choice of exchange for both traders and policymakers. In addition, I observe a growing interest in the design of pricing functions for CEXs and DEXs, particularly in the area of automated market makers (AMMs). Finally, based on my findings, I outline future research opportunities in this context and derive research gaps as well as recommended actions for practitioners.

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Introduction

In recent years, the cryptocurrency market has undergone a remarkable transformation, evolving from an obscure realm of tech enthusiasts into a global financial ecosystem of significant importance (Bouri et al., 2019 ). This evolution has been underpinned by technological advancements and innovations, with both centralized exchanges (CEXs) and decentralized exchanges (DEXs) emerging as critical factors in shaping the market’s trajectory. With the surpassing of a monthly trading volume of over $4,000B on CEXs and over $200B on DEXs in May 2021, spot trading on CEXs and DEXs reached its peak, increasing more than sevenfold within half a year, as can be seen in Fig.  1 . In the subsequent months of the cryptocurrency bull run of 2021, DEXs experienced proportional more growth in their share of trading volume on cryptocurrency markets then their central counterpart, which could be attributed to the launch of UniswapV3, one of the most successful DEX nowadays (Adams et al., 2021 ; Hashemseresht & Pourpouneh, 2022 ). Since the beginning of 2022, the volume appears to be declining on both CEXs and DEXs, with DEXs showing a comparatively smaller decrease in trading volume compared to CEXs. One reason for this could be, in part, the unexpected insolvency of the CEX FTX in November 2022, which caused general uncertainty in the cryptocurrency market (Yaffe-Bellany, 2022 ) and compelled CEXs to improve the transparency in managing their customer funds in order to regain or strengthen their customer’s trust (Li, 2023 ).

Spot trading volume on CEXs (left) and DEXs (right) from September 2020 to September 2023 based on data obtained from The Block ( 2023a ) and The Block ( 2023b )

The inception of CEXs and DEXs can be traced back to the early days of cryptocurrency trading. Centralized exchanges, like the infamous Mt. Gox (Greenberg, 2014 ; Mohan, 2022 ), established the initial framework for trading cryptocurrencies against traditional fiat currencies. While these platforms played a crucial role in the market’s inception, they displayed vulnerabilities to security breaches, regulatory oversight, and operational limitations (Caliskan, 2020 ; Chohan, 2022 ). Concurrently, the concept of DEX emerged as a response to the inherent limitations of CEX (Lo & Medda, 2020 ). The core principle behind DEX was to create trusted, peer-to-peer platforms that give users control over their private keys and assets (Dai, 2020 ). However, it was not until the advent of Ethereum’s smart contract functionality that DEX began to demonstrate substantial viability. Uniswap, an Ethereum-based DEX, emerged as one of the most successful projects into this domain (Adams, 2018 ; Koroļkovs & Kodors, 2022 ), diverging from and evolving the automated market-making (AMM) model previously implemented by the Bancor protocol (Hertzog et al., 2017 ; Ottina et al., 2023 ). Uniswap with its V2 later became the first DEX to surpass a daily trading volume of over $1B on October 26, 2020 (Adams, 2018 ; DefiLlama, 2023 ), and conducted one of the most successful token airdrops to date (Makridis et al., 2023 ).

Meanwhile, the cryptocurrency exchange ecosystem in the cryptocurrency markets has expanded considerably. Notably, DEXs have surpassed their centralized counterparts in numbers, with ~ 500 DEXs compared to ~ 300 CEXs as of October 2023 (CoinGecko, 2023 ). This trend can mainly be attributed to the relative ease with which DEXs can be distributed and established. For example, the once leading DEX, SushiSwap, started as an emulation of its competitor, Uniswap (Wang, 2022 ). Nevertheless, what sometimes began with mere imitations has — like CEXs — since transformed into a diverse range of distinct protocols, encompassing various economic relationships such as cryptocurrency trading, cryptocurrency barter, or even cryptocurrency banking. As a result, categorizing and differentiating the complexities represented by these protocols with the definitions provided by the existing academic literature often proves challenging due to the evolving nature of the cryptocurrency exchange industry. For instance, Xia et al. ( 2020 , p. 2) define CEXs as exchanges, which are “governed by a company or an organization” while DEXs “provide automated process [emphasis added] for peer-to-peer trades.” However, there are a lot of DEXs using their governance tokens like UNI, SNX, or BAL to make decisions regarding the protocol and thereby act as a decentralized autonomous organization (DAO) (Wang et al., 2023 ) that could be categorized as CEXs with this definition. Additionally, there are also some CEXs like Binance ( 2023 ) that offer P2P trades to their customers, which could be automatized using API bots and therefore may apply as DEXs depending on the interpretation of automated processing in the aforementioned definition. Some of the academic works also list hybrid (cryptocurrency) exchanges (HEX) as an alternative to the strict differentiation between CEXs and DEXs (e.g., Luo et al., 2019 ; Qin et al., 2021 ). However, they specify either not at all or only very imprecisely what characteristics a cryptocurrency exchange must have to be classified as a HEX. For instance, Luo et al., ( 2019 , p. 48) only give the information that “a HEX maintains a centralized database to provide matching services for the traders, while all transactions are still executed by smart contracts hosted in a blockchain.” With a definition like this, it raises the question, especially, to what extent centralization of a database suffices as a criterion to no longer be considered a DEX, particularly since many DEXs also provide a certain form of a central database through their user interfaces in the form of a website, and sometimes, matching services as well (Brasse & Hyun, 2023 ). For example, the exchange 1inch offers traders the possibility to set limit orders using their web interface, which gets managed and operated by the 1inch Foundation (1inch, 2023 ), a NPO and DAO. In accordance with the previous definition, it would be necessary to determine to what extent a DAO or NPO should indeed be classified as a criterion for a HEX. In academic literature, however, 1inch is classified as a DEX despite the presence of a central database (Boonpeam et al., 2021 ; Cola et al., 2023 ; Kitzler et al., 2023 ; Xu et al., 2023 ). The blurred distinction between CEXs and DEXs, especially HEXs, reflects the diversity of exchange concepts in the cryptocurrency market and academic literature. This calls for a systematic elaboration of the characteristics and dimensions of cryptocurrency exchanges and the development of a classification framework.

For this reason, I conduct a secondary study in the form of a review of the literature on cryptocurrency exchanges, acknowledging the complexities of both CEXs and DEXs, but focusing primarily on the marketized processes within them as their most prominent use case. Here, a systematic review approach is particularly advisable due to the diversity of published literature on the topic of CEXs and DEXs. In addition, it allows for a consolidation of the current state of research and facilitates the drawing of conclusions from a condensed pool of information, which is valuable due to the comprehensive insights it provides. First, I identify and analyze existing papers on CEXs and DEXs using a systematic method, focusing on their mentioned characteristics as well as the dimensions explored by the academic literature. This enables a downstream analysis of popular topics and helps to identify promising research gaps. A systematic literature review combines results from different methodical approaches into a unified contribution, thereby reducing the impact of subjectivity associated with individual articles. To the best of my knowledge, there are only two (systematic) reviews in the literature that focus on CEXs and DEXs. Eigelshoven et al. ( 2021 ) use a systematic approach to investigate the vulnerability of the CEX and DEX to market manipulation. In their conference paper, they identify seven manipulation methods and six indicators of the success of market manipulation schemes. However, a detailed differentiation between CEXs and DEXs and their characteristics is missing. The final sample size of 38 is also rather limited. On the other hand, Y. Chen et al., ( 2023b ) focus their research report on the cryptocurrency trading infrastructure, differentiating between CEXs and DEXs. However, their work is primarily focused on collecting survey results rather than systematically capturing current research in the cryptocurrency exchange space. Consequently, it does not reach the depth of a systematic literature review. Thus, there is a need for a new, in-depth investigation to systematize the exchange landscape in the cryptocurrency market.

The remainder of this paper is organized as follows. The “ Methodology ” section provides an overview of the proposed methodology, followed by a description of the design of the conceptual framework. This framework uses several superordinate terms to assess the current state of research on CEXs and DEXs. The “ Descriptive analysis of the literature sample ” section presents and analyzes the descriptive characteristics of the literature in the literature sample. The “ Discussion of the secondary study results ” section discusses the findings in the context of the established framework, delving into the characteristics, advantages, and disadvantages of different cryptocurrency exchanges and formally defining CEXs and DEXs. The “ Open research questions and future directions ” section highlights the potential research directions that have emerged from the analysis of the literature sample. Finally, the “ Conclusion ” section summarizes the conclusions of the study and discusses the implications and limitations of the research.

Methodology

Literature search and selection strategy.

Secondary studies, such as literature reviews, require a comprehensive and reliable sample of literature to ensure that readers can thoroughly evaluate and understand research findings (Sauer & Seuring, 2023 ). The primary goal of a literature review is to organize the existing literature on a topic in order to examine the current state of research and identify any existing research gaps (Grisar & Meyer, 2016 ). Literature reviews are conventionally categorized into four distinct types: narrative reviews, scoping reviews, systematic reviews, and meta-analyses, each distinguished by their approach for assembling a literature sample (Hochrein & Glock, 2012 ). Narrative reviews do not explain the development of their literature sample and often fail to methodically document the literature search process, making it difficult or even impossible for readers to replicate the findings, especially when the research results depend on the selection of reviewed articles within a particular research area (Massaro et al., 2016 ). In contrast to narrative reviews, scoping reviews aim to identify and describe the available evidence on a particular topic, with a particular focus on clarifying key concepts and definitions found in the relevant literature. They delve into the methods used to research a particular topic or field, and seek to uncover and analyze any prevailing gaps in knowledge (Munn et al., 2018 ). Due to their exploratory nature, scoping reviews often serve as a precursor to systematic literature reviews, which use a systematic method to generate a literature sample (Paul et al., 2021 ). The fundamental aim of a systematic literature review is to provide a structured, comprehensive, and truthful overview of the current state of the art. Consequently, systematic reviews are considered to be the most unbiased form of literature review. It is not uncommon for data from systematic reviews to be extracted and subsequently used as the basic framework for conducting a meta-analysis (Hägele et al., 2023 ). Finally, meta-analyses primarily use statistical techniques to evaluate an existing sample of literature, making them primarily quantitative in nature (Snyder, 2019 ). My method is designed to systematically identify the research dimensions of CEX and DEX research in cryptocurrency markets. To achieve this, I conduct a systematic literature search following the methods outlined by Denyer and Tranfield ( 2009 ), Stone and Rahimifard ( 2018 ), and Hägele et al. ( 2023 ) to identify relevant literature review articles. As shown in Fig.  2 , the approach follows five sequential steps that are condensed into the systematic research method used to specify the literature sample.

Developing research questions: the first step focuses on formulating research questions that will guide the systematic literature review. This is done with a particular emphasis on the research objective, which is to determine the dimensions of research related to CEXs and DEXs. Therefore, the following questions are specified:

RQ1: What is the current understanding of CEXs and DEXs in the literature? Is there a common definition or does the understanding vary widely?

RQ2: What CEX and DEX dimensions are addressed in the literature? Is it possible to identify a particular research focus or trending topics in the cryptocurrency exchange literature? Are some dimensions less or not focused on, thus creating research gaps?

RQ3: What are the pricing features currently used in CEXs and DEXs? Are they similar, or are there variations that only exist on one of the two cryptocurrency exchanges?

Database search and retrieval: the next step is to systematically search the current academic literature for relevant papers. This is done by brainstorming and defining appropriate keywords that are directly related to the research topic, without claiming to be exhaustive. Variations of the keywords are then added to the pool to account for differences in spelling. Finally, the keywords are divided into two groups and linked within each group using the logical operator OR, while both groups are linked together using the logical operator AND. The resulting search string is then used in scientific databases such as Ebsco Host, Elsevier, Emerald, Google Scholar, Springer Link, Web of Science, and Wiley Online. The search is conducted in October 2023 and includes all publications up to September 2023. The groups defined and the keywords used are shown in Table  1 .

Screening and selection: in this step, the literature is systematically reviewed for alignment with the research objectives using the PRISMA approach (e.g., Rethlefsen et al., 2021 ), as shown in Fig.  3 . For each paper suggested by the database search, the first step is to check whether it is already part of the literature sample. If not, the abstract of the paper is reviewed to assess its suitability for addressing one or more of the research questions. If suitability cannot be determined from the abstract, the full paper is read and a decision is made whether or not to include it in the sample. After reviewing the database results, the literature cited in the sample papers is also reviewed for eligibility, thus initiating a snowball research process. After reading the initially identified 143 articles, 89 articles remained as the size of the literature sample. Some articles were excluded because they focused more on decentralized finance (DeFi) rather than on DEXs or CEXs (e.g., Schueffel, 2021 ), or because they appeared to lack sufficient scientific rigor.

Data extraction and synthesis: after selecting the articles, a critical review is conducted to capture the essential characteristics, central messages, and concepts of the literature sample. Essential information for answering the research questions is captured, while a framework is developed to facilitate categorization and structuring. This framework is iteratively adapted, revised, and developed during the paper review process, ultimately allowing for a systematic representation of the dimensions of CEX and DEX research, as well as the identification of interrelationships, interactions, and research gaps. In addition to content-specific aspects, descriptive characteristics of the papers are also captured to provide a systematic literature review; to gain insight into the origin, distribution, and development of research on the topic; and to provide a foundation for future research building on this work.

Reporting and critical appraisal of research findings: in the final step, the collected findings are integrated into the framework and condensed for clarity. Information is cross-referenced across research questions to identify superordinate relationships. Finally, the findings are visually presented in an aesthetically pleasing manner for a compact yet informative presentation. A summary of all information collected is also included in Appendices A and B .

Literature search and review method adapted from Denyer and Tranfield, ( 2009 ), Stone and Rahimifard ( 2018 ), and Hägele et al. ( 2023 )

Process of literature selection based on the PRISMA approach following Denyer and Tranfield ( 2009 ), Stone and Rahimifard ( 2018 ), and Hägele et al. ( 2023 )

Framework development

The goal of the framework development is to systematically capture the dimensions of CEX and DEX research. To achieve this, the first step was to identify and formulate appropriate superordinate terms to facilitate a structured comparison of the characteristics of CEXs and DEXs. The starting point for this objective is to first establish a basic understanding of CEXs and DEXs in cryptocurrency markets. For this reason, all definitions of CEXs and DEXs mentioned in the literature sample are first recorded. Often, these are not explicitly labeled as definitions, which require a clear distinction between characteristics and definitions. In addition, the papers often lack precise or only vague definitions of DEXs and especially CEXs. Therefore, for better comparison, only those papers with definitions that explicitly cover both CEX and DEX are presented in Table  2 . However, all identified definitions of CEXs and DEXs can also be found in Appendix B .

When identifying definitions, only language that explicitly named or referred to CEXs or DEXs was considered a definition. Definitions that were not specific to the exchange models, such as “a cryptocurrency exchange is a marketplace where users can buy and sell cryptocurrencies” (Xia et al., 2020 , p. 2), were also not included because the focus of this paper is on addressing the research questions and differentiating between CEXs and DEXs. Interestingly, the papers in the literature sample often define specific implementations of DEXs, such as AMMs, without first explaining what a DEX is. When DEXs are defined, it is often in the context of distinguishing them from CEXs, without explicitly outlining what defines a CEX (e.g., Berg et al., 2022 ; Falakshahi et al., 2021 ; Fritsch, 2021 ; Jeong et al., 2023 ). Furthermore, there are cases where terms such as DeFi and DEXs, although conceptually related, are still used interchangeably (Aigner & Dhaliwal, 2021 ; Shah et al., 2023 ). Overall, CEXs are defined much less frequently than DEXs. Only 27 out of 89 papers, or about 30% of all papers in the literature sample, provide a definition for CEXs. Conversely, at least 39 out of 89 papers, or more than 44%, define DEXs. Reasons for this could be the publication date of the papers in the literature sample and the relative novelty of DEXs compared to CEXs. Therefore, the focus is often on the former, while the understanding of the latter, which has been around longer, is assumed to be known.

In addition to collecting and consolidating definitions of CEXs and DEXs, an analysis of the keywords used in the papers from the literature sample is also conducted as part of the framework development. The aim is to gain insight into the methodical focus of the papers and, more importantly, to gather information about their thematic focus in order to identify possible research directions. A total of 306 keywords were extracted from the papers in the literature sample, although not all papers used keywords. The average number of keywords per paper is therefore approximately 3.4, reflecting considerable diversity in keyword selection. After removing keywords that were used in multiple papers, 162 unique keywords remained, which were then further condensed into appropriate categories (see Table  3 ).

Looking at the absolute frequency of keywords within each category (including repetitions across papers), certain research directions can already be deduced. The focus of the papers from the literature sample seems to revolve around some less surprising category emphases, such as cryptocurrencies, financial markets, or finance in general. However, there is also a notable concentration of papers using keywords related to market infrastructures such as DeFi protocols (e.g., Shah et al., 2023 ) or networks (Kitzler et al., 2023 ), especially in the context of market design and, more specifically, pricing functions (e.g., Aoyagi, 2020 ; Koroļkovs & Kodors, 2022 ).

After studying the definitions of CEXs and DEXs in the papers from the literature review, I was able to determine both the current understanding of these terms in the academic literature and identify initial trends and emphases through the collection and consolidation of keywords. The next step is to develop a structured and comprehensible framework based on these findings. In the context of the contribution, especially to answer research question 2, superordinate terms are derived for the framework that allow different perspectives on the study of CEXs and DEXs and reflect the frequency of different keyword uses (excluding methodical keywords). As keywords, particularly from the financial domain, were mentioned more frequently, they were subdivided into several superordinate terms: Market Efficiency , Liquidity Provision , and User Experience . From the category of cryptocurrencies and blockchain (see Table  3 ), the superordinate term Technological was chosen to allow for a broader and multifaceted categorization. The aspects of security and ethics from the keyword categorization are adopted with minimal changes as Security and Trust , since “trust” and trust-related terms seem to be mentioned more frequently in the literature sample. Finally, a certain regulatory context can be derived from the definitions of CEXs and DEXs. Therefore, the last superordinate term introduced is Regulatory to cover all kinds of legal aspects. Figure  4 provides a summary of the derived superordinate terms for the dimensions of CEX and DEX research.

Superordinate terms for the dimensions of CEX and DEX research

Once the superordinate terms have been formulated, the systematic and thorough research of the dimensions of CEX and DEX can begin. To accomplish this, the literature sample is searched for statements related to the specified superordinate terms, and these statements are assigned accordingly. In the comprehensive summary of all statements on the dimensions (see Appendix C ), whenever the context allows, a corresponding statement is captured as faithfully as possible. When a verbatim categorization would not make sense due to lack of context, the statement is paraphrased and then recorded. Sometimes statements could theoretically be assigned to multiple categories, for example, “Users can access that liquidity and exchange tokens based on a pricing function dictated by their relative availability in the pool” (Palit, 2022 , p. 2). In such cases, these statements are assigned to the category with which they most closely align, even if they could also be assigned to another category. This compromise is made to avoid duplication, although it introduces a degree of subjectivity. After all papers in the literature sample have been critically analyzed, the framework is well populated and it is possible to proceed with the cross-category and cross-exchange analysis. All steps of the framework design, from the systematization of definitions and keywords to the derivation of the superordinate terms of the framework and the description of the assignment of statements, are summarized once again in Fig.  5 .

Summary of the framework development steps

Descriptive analysis of the literature sample

The literature sample consists of 89 review articles on CEXs and DEXs, all of which were published in the years 2019–2023 (or have yet to be published in the case of preprints). At first glance, this narrow publication window may seem unexpected, especially given that no specific restrictions on publication years were imposed during the database search. While the whitepaper for Bitcoin, the first cryptocurrency, was published by Satoshi Nakamoto in 2008 (Nakamoto, 2008 ), and the foundation for today’s DEXs was laid with the Ethereum whitepaper in 2013 (Buterin, 2013 ), the initial breakthrough of CEXs, and in particular DEXs, remained elusive to the general public until the launch of Uniswap V2 in 2020 (Adams et al., 2020 ). Consequently, the narrowed publication timeframe of the papers in the literature sample can also be attributed to a surge of scholarly interest in shaping and understanding these novel marketplaces. During this specific publication period, a rapid increase in the number of publications per year can be observed, as shown in Fig.  6 , which summarizes all the descriptive characteristics of the literature sample. In addition to the rapid increase in annual publications on CEXs and DEXs, a diversity in the countries of origin of the authors of the papers in the literature sample can also be observed. The literature sample includes more than 280 authors from more than 30 different countries, with the majority coming from the USA, followed by the UK, China, Switzerland, and Canada. The diversity of countries of origin, including smaller nations such as St. Lucia, reflects the international importance of research on CEXs and DEXs and underscores the timeliness and relevance of the topic. All countries of origin with at least 10 authors are also shown in Fig.  6 .

Descriptive characteristics of the literature sample

The novelty of the papers is also reflected in the type of publication. More than a third of the papers in the literature sample are preprints, most of which have been published either on SSRN or arXiv. While the scientific quality of these papers is not necessarily guaranteed, they have the highest degree of timeliness that a paper can have. In the selection of preprints, care was also taken to ensure their professionality and active further development. In contrast to preprints, and in terms of quantity, the second and third most common types are journal articles and conference papers. They make up more than half of all papers in the literature sample and attest to the scientific quality of the results of the literature search. In addition, the relatively high proportion of conference papers again supports the timeliness of the subject, as it appears that a significant part of scientific discourse is still conducted within conference communities. Similarly, the limited number of book chapters, let alone book publications, reflects the early stage of research on CEXs and DEXs in cryptocurrency markets.

Finally, the methods of the papers in the literature sample were examined in more detail and classified into seven categories (see also Fig.  6 for reference). These categories do not claim to cover all possible scientific methods, but rather attempt to provide a finer distinction than the classical distinction between quantitative and qualitative methods. Therefore, it is also possible for a paper to be associated with more than one method. Since cryptocurrency markets as a research discipline tend to be at the intersection of several scientific disciplines, I refrain from differentiating the methods of the papers in the literature sample into more distinct theoretical approaches belonging to different scientific disciplines, as such a differentiation may not be helpful and consistent if no more than half of the papers could be categorized by it. However, I acknowledge that there are different, more fine-grained economic approaches (neoclassicism, ANT approach, behavioral economics, …) to the study of markets that could be differentiated and are applied by some of the papers in the literature sample. Looking at the categorization used, the first thing that stands out is the very high proportion of quantitative research compared to qualitative research. More than three quarters of all papers use a mathematical approach, which in most cases is also related to modeling, the second most common research method. The reasons for this can be attributed to the financial nature of the subject matter. As the categorization of keywords has already shown, CEXs and DEXs are primarily financial constructs, and their conception is therefore predominantly quantitative in nature. In addition, there may be a monetary aspect to the design of CEXs and DEXs. The recent success of many companies or projects using CEXs and DEXs has made it easier to investigate the reasons for the success or failure of individual CEX and DEX models. Furthermore, a closer look at the content of the literature sample reveals that, especially in the case of DEXs, their design is still actively researched, with a focus on optimization (e.g., Bergault et al., 2023 ; Krishnamachari et al., 2021 ). This thesis is further supported by the high proportion of conceptual methods in the literature sample, which involve the development of innovative approaches that advance current research. These papers are typically highly technical in nature and aim to advance existing approaches through detailed and innovative solutions. Another significant proportion of the papers in the literature sample, in contrast to the methods discussed so far, use existing historical data to gain new insights. These papers often try to identify indicators from market data of a certain period, based on specific events such as the insolvency of the CEX FTX or the collapse of the stablecoin TerraUSD (e.g., Milunovich & Lee, 2022 ; Vidal-Tomás et al., 2023 ), with the aim of improving the predictability of the occurrence of such disasters in the future. In contrast to conceptual papers, empirical papers primarily serve the purpose of deriving policy recommendations and concepts, but do not focus on demonstrating their actual implementation. One of the least prevalent methods in the literature sample is qualitative, especially in literature reviews such as this one. While there may be numerous approaches to advancing the current state of research based on the high proportion of conceptual and quantitative research, this advancement is rarely qualitatively grounded, possibly due to the novelty of the research topic. This, in turn, reinforces the purpose of this paper.

Finally, special attention should be paid to those papers in the literature sample that are of high importance for research in the field of CEXs and DEXs, either because of their high number of Google Scholar citations or because they are particularly well-founded through their extensive literature references. The papers with the most Google Scholar citations at the time of the literature review include (in order from most to least cited) Schär ( 2021 ), Daian et al. ( 2020 ), and Lee ( 2019 ). While the early appearance and fundamental orientation of all these papers may be the reason for their high citation rate, in the case of the middle one it is certainly due to the systematic discovery of opportunistic behavior of market participants on the DEXs and the associated practice of front-running at the expense of other market participants, which had not been observed to this extent until then. Nevertheless, all of these articles can be considered highly relevant to the study of CEXs and DEXs. Xu et al. ( 2023 ), Qin et al. ( 2021 ), and Sai et al. ( 2021 ) have the most extensive literature base among the papers in the literature sample. The research approach of all three papers is to conduct a thorough literature review. By delving into the existing literature, they build a solid foundation of knowledge that allows them to place their work firmly in the context of CEX and DEX research. Researchers building on these foundational references can use the insights and critical analysis provided to further their own investigations and contribute to the ongoing advancement of knowledge in the field.

Discussion of the secondary study results

A critical analysis of the papers in the literature sample goes beyond just capturing descriptive characteristics; it delves into the multifaceted landscape of research dimensions on CEXs and DEXs. These dimensions are thoughtfully categorized under their corresponding superordinate terms within the framework and organized in a tabular format, as you can see in Appendix C . However, in an effort to present the findings in a clear and concise manner and to answer the second research question, I have further condensed the dimensions under each superordinate term into highly aggregated statements, as shown in Table  4 . These statements have been carefully formulated to ensure that they encompass the full range of dimensions identified, while maintaining clarity and eliminating redundancy. The exact references are still included in Appendix C . However, for the sake of brevity, I will refrain from including them here. As I proceed, the following sections will examine each dimension in more detail under its respective superordinate term, providing a comprehensive examination and comparison of the dimensions of research on CEXs and DEXs. Based on the results of the secondary analysis, I will then derive precise definitions for CEXs and DEXs, using the newly gained insights and the underlying rationale of these dimensions within the CEX and DEX research landscape.

Looking at CEXs and DEXs from a technological perspective, there are distinct features and characteristics that set these two approaches apart. CEXs provide an easy-to-use, centralized platform for cryptocurrency trading. A notable advantage lies in their order-book-based system, which simplifies trading by allowing users to trade cryptocurrencies against traditional fiat currencies fiat currencies untethered from the underlying blockchain (Aigner & Dhaliwal, 2021 ). This streamlining of the trading process is further supported by the use of “hot” wallets for faster access to funds (Johnson, 2020 ). It is important to note, however, that CEXs are not without their drawbacks, including occasional technical delays and server outages that can hinder the seamless execution of trades (Lim, 2023 ). On the other hand, DEXs are emerging as an innovative alternative. They operate without central authorities and enable peer-to-peer trading by using smart contracts for transactions, all without requiring users to relinquish custody of their tokens (e.g., Aoyagi & Ito, 2021 ). This is a notable advantage, as it aligns with the ethos of decentralization and puts users in control of their assets. DEXs also employ automated market-making functions, typically in the form of constant function market makers (CFMMs), which emphasize efficiency and reduced storage requirements (Angeris, et al., 2022a ). Nevertheless, DEXs may face problems related to front-running, where traders with advanced knowledge can use the order of transactions to their advantage (Park, 2021 ).

From a regulatory perspective, CEXs’ adherence to federal and state laws seems to provide a sense of legitimacy and security. However, it is important to recognize that these regulations are often focused on traditional financial instruments and may not be perfectly suited to the rapidly evolving landscape of cryptocurrencies. Furthermore, the inherent anonymity of traders and the lack of official oversight create a breeding ground for activities such as wash trading and price manipulation (Alexander et al., 2023 ). This not only compromises the integrity of these exchanges but also exposes users to a higher risk of financial loss (Aspris et al., 2021 ). In contrast, DEXs prioritize global accessibility and anonymity, bypassing Know Your Customer (KYC) and Anti-Money Laundering (AML) regulations (Aspris et al., 2021 ). This approach can be seen as a double-edged sword. On the one hand, it opens the door to a wider range of listings and cross-border trading opportunities (Dewey & Newbold, 2023 ). On the other hand, it raises concerns about potential money laundering and illicit financial activities (Dai, 2020 ). The increased anonymity of DEXs may make them an attractive platform for individuals seeking to engage in these activities.

When trading cryptocurrencies, aspects of security and risk are of high importance. Traders on CEXs are exposed to a number of vulnerabilities, making it imperative to entrust assets to the infrastructure of the CEX (Lim, 2023 ). These risks include concerns such as insider trading, hacking incidents, price manipulation, fraud, data breaches, and even outright theft (Johnson, 2020 ). The need for trust in the operational integrity of the CEX becomes a central element of any transaction. On the other hand, DEXs prioritize security and privacy by eliminating centralized control and providing greater transparency and the ability to retain full custody of assets, effectively reducing counterparty risk (Alexander et al., 2023 ; Lin, 2019 ). DEXs facilitate peer-to-peer trading, allowing participants to exchange on-chain assets without relying on a centralized authority (Angeris & Chitra, 2020 ). However, DEXs have also increasingly become a preferred platform for liquidating stolen tokens due to the anonymity and trustless nature of smart contract transactions (Aspris et al., 2021 ). This, in turn, presents a different type of security concern within the DEX environment.

Providing liquidity on a CEX and a DEX presents different sets of advantages and disadvantages, each catering to different preferences and risk tolerances. On a CEX, as the primary marketplace, it provides an easy way for users to transfer currencies with high liquidity (Y. Chen et al., 2023b ). This liquidity is primarily driven by the constant interaction between buyers and sellers. However, it is worth noting that CEXs, in an effort to maintain market integrity, often impose strict criteria for listing assets (Qin et al., 2021 ). This can lead to delays in the cryptocurrency listing process and limit the range of tokens available for liquidity provision (Lin, 2019 ). On the other hand, when it comes to DEXs, liquidity providers take on a unique role. They earn fixed commissions per trade, accepting market risk in the process, making it an enticing opportunity for those who thrive on the decentralization ethos (Aigner & Dhaliwal, 2021 ). The process of adding tokens to DEXs is significantly more accessible, with fewer barriers compared to CEXs (Dewey & Newbold, 2023 ). In fact, any token holder can become a liquidity provider simply by depositing tokens. However, the provision of liquidity in AMMs on DEXs works differently. It is determined by the ratio of tokens in the pool and does not actively contribute to price discovery (Y. Chen et al., 2023b ). Unlike CEXs, where price formation and especially discovery is primarily driven by order book dynamics, DEXs rely on the inherent token ratios in the pools.

Trading on a CEX is, from a user’s experience , a structured process in which assets move from a user wallet to a wallet managed by the exchange (Victor & Weintraud, 2021 ). This arrangement has both advantages and disadvantages. On the positive side, CEXs offer relatively fast transaction speeds, enriched trading functionalities, and a user-friendly interface (Lim, 2023 ). These aspects make for an efficient and convenient trading experience, allowing users to execute their transactions with ease. However, trading on CEXs is also associated with high transaction fees, which reduce the overall returns (Dai, 2020 ). In addition, CEXs tend to have limited transparency. Users may find it difficult to obtain comprehensive information about the inner workings of the exchange, which can lead to traders’ discomfort. In addition, CEXs often require complex registration procedures, which can deter potential users and complicate the onboarding process (Lin, 2019 ). In contrast, DEXs allow users to engage in asset exchanges without the involvement of intermediaries and guarantee that transactions are recorded on a public ledger (Aspris et al., 2021 ). This open and decentralized approach ensures a transparent and secure environment for users. However, DEXs are susceptible to transaction-ordering attacks, which can affect the order and thus the profitability of trades (Han et al., 2022 ). AMM aggregators provide flexibility by not requiring specific pairings for transactions, but they can occasionally lead to suboptimal pricing (Park, 2021 ). Despite these challenges, DEXs offer an attractive advantage in reducing trading costs, especially for large orders (Lin, 2019 ).

Finally, market efficiency at CEXs depends on several key factors. First and foremost, despite their comparative efficiency, CEXs often face constraints, particularly limited trading volume and liquidity. This can hinder the seamless execution of trades, making them less efficient at handling large order flows (Wang & Krishnamachari, 2022 ). In addition, price determination on CEXs relies solely on the order book trading process and trader control, resulting in potentially significant price volatility (Ciampi et al., 2022 ). The control factor can lead to potential price manipulation and erratic fluctuations that can undermine market stability. Conversely, CEXs also have some advantages. They encourage the active participation of market makers, an essential component in maintaining order flow and liquidity. This, in turn, encourages a diversified range of cryptocurrency transactions and provides traders with a degree of predictability and ease in executing their trades (Schär, 2021 ). DEXs, on the other hand, contribute to price discovery by facilitating the listing and trading of new tokens (Aspris et al., 2021 ). However, prices on DEXs tend to be less efficient, resulting in inconsistencies and variations across DEX platforms (Barbon & Ranaldo, 2021 ). This inconsistency can pose challenges for traders seeking price transparency and accurate execution. DEXs primarily support crypto-to-crypto transactions and rely on arbitrageurs to balance prices, which can lead to longer execution times and potential inefficiencies (Krishnamachari et al., 2021 ). However, DEXs do offer unique benefits by more efficiently allocating risk among traders with different risk preferences, resulting in distinct trading advantages.

In summary, the findings on the dimensions of CEX and DEX research, as determined in this manner and viewed from multiple perspectives, can be summarized as follows, in accordance with the previously explored definitions and keywords identified to answer the first research question:

Centralized exchanges (CEXs) are cryptocurrency trading platforms that provide a user-friendly and centralized environment for buying and selling digital assets. They use an order book-based system to simplify the trading process and allow users to trade cryptocurrencies against traditional fiat currencies. However, technical delays and server outages can occur, potentially disrupting the smooth execution of transactions. CEXs primarily comply with federal and state regulations, providing users with a sense of authenticity and security. However, the anonymity of traders on some CEXs raises concerns about activities such as wash-trading and price manipulation, which can undermine the integrity of these exchanges.

Decentralized exchanges (DEXs) operate without a central authority and enable peer-to-peer cryptocurrency trading by using smart contracts for transactions, allowing users to retain custody of their tokens. DEXs include automated market-making functions, typically in the form of constant function market makers (CFMMs), which increase efficiency and reduce the need for extensive on-chain storage. DEXs face challenges such as front-running, where traders with advanced knowledge take advantage of the transaction order. In addition, they prioritize global accessibility and anonymity, bypassing KYC and AML regulations, which can expand the scope of listings but also raise concerns around money laundering and illicit financial activity.

Open research questions and future directions

Within the vast landscape of cryptocurrency exchanges, it has become clear that researchers are actively engaged in exploring a variety of aspects, each of which offers unique insights. One of the key areas of research is the concept of pricing functions that underpin the operation of these exchanges (e.g., Park, 2021 , 2023 ). These vary not only between CEXs and DEXs but also within the emerging category of HEXs, such as EtherDelta, dYdX, and IDEX (dos Santos et al., 2022 ; Falakshahi et al., 2021 ; Koroļkovs & Kodors, 2022 ; Schär, 2021 ). In Fig. 7 , I provide a visual systematization of the different exchanges and categorize them according to their pricing functions mentioned in the literature sample to answer the third research question. In addition, I also provide implementation examples that exist in cryptocurrency markets for each different implementation variant. To the best of my knowledge, it is the first differentiation of such pricing functions and therefore may not capture all possible concepts already implemented in practice. However, it attempts to capture the most prominent ones.

Pricing functions of cryptocurrency exchanges

As shown in the figure, the pricing mechanisms of an exchange can first be differentiated by considering whether price discovery takes place on-chain, specifically on a cryptocurrency’s blockchain using smart contracts, or off-chain. While the on-chain method has the well-known advantages and disadvantages associated with a blockchain, such as a high level of transparency but increased storage costs and slower transaction processing, an off-chain implementation offers speed but tends to be more centralized and less transparent. In addition to the well-known central limit order book (CLOB), which “is a method to facilitate an exchange between market participants, where two sorted lists are maintained including the price and amount that traders are willing to buy (bid side) or sell (ask side)” (Khakhar & Chen, 2022 , p. 1), and traditional auction trading, a family of pricing functions based on the logarithmic market scoring rule developed by Hanson ( 2003 , 2007 ) has received increasing attention in research. These pricing functions were first proposed for implementation on Ethereum by Vitalik Buterin in a 2016 Reddit post (Buterin, 2016 ) and can be subsumed under the term of AMMs. Unlike CLOB pricing functions and auctions, which are less prepared for on-chain use due to the associated blockchain storage costs (Zatonatska et al., 2022 ), but can still be implemented on-chain, AMMs are only implemented on-chain. Therefore, by definition, they are used exclusively by HEXs and DEXs. In the category of AMMs, there are a variety of models, such as constant function market makers (CFMMs), which further branch into liquidity sensitive logarithmic market scoring rule (LS-LSMR), constant product market maker (CPMM), constant sum market maker (CSMM), constant mean market maker (CMMM), and proactive market maker (PMM). Although these models differ in minor details, they all aim to optimize liquidity provision and price discovery in the context of DEXs. The diversity of approaches and methods is a testament to the volatility of concepts in this area of research. Many trades on DEXs currently occur under suboptimal conditions (Berg et al., 2022 ), imposing negative externalities on other DeFi applications (Capponi & Jia, 2021 ). While the current research focus is on the development of new on-chain pricing mechanisms (Bergault et al., 2023 ; Krishnamachari et al., 2021 ), off-chain settlement is increasingly taking a back seat, and thus, a clear research need can be identified.

DEXs are still dependent on external prices (Jensen et al., 2021a ; Sylvester et al., 2022 ), which is why there is a growing focus on improving market efficiency and price discovery of DEXs (e.g., Alexander et al., 2023 ; Barbon & Ranaldo, 2021 ; Berg et al., 2022 ; Pourpouneh et al., 2020 ). New and innovative pricing functions are already being actively researched (e.g., Y. Chen et al., 2023b ; Kim et al., 2022 ; Lin, 2019 ; Schär, 2021 ). One solution could be the use of oracles (Berg et al., 2022 ; Dave et al., 2021 ), which is still an object of active development. Another topic of particular interest in current research is the design of front-running resistant AMMs (e.g., Bartoletti et al., 2022 ; Ciampi et al., 2022 ; Zhou et al., 2021a , b ). Front-running, or the act of exploiting advance knowledge of upcoming transactions, remains a concern in DeFi. Researchers are actively investigating ways to improve security mechanisms to protect users from such unfair trading practices. The sequencing of transactions within DEXs is also of paramount importance, as it affects the fairness and efficiency of order execution. Researchers are actively working to improve the algorithms that govern the execution of trades in DEXs (e.g., Gong & Kate, 2023 ). It is important to make DEXs resilient to order-routing and front-running in order to maintain their competitiveness with CEXs. For this reason, future research, while already very active, needs to focus on advancing existing approaches to ensure this.

AMMs are at the forefront of research and offer the potential to provide liquidity more efficiently than CEXs. Liquidity providers on DEXs must balance potential adverse selection with fee income, raising questions about their strategies and returns (Lehar & Parlour, 2021 ). Quantifying the returns of liquidity providers is another topic that has received much attention in the literature (e.g., Aigner & Dhaliwal, 2021 ; Bergault et al., 2023 ; Khakhar & Chen, 2022 ; Milionis et al., 2023b ). Among other things, liquidity provision on DEXs has been found to be influenced by other liquidity providers (Aoyagi, 2020 ) and other markets (e.g., CEXs) (Aoyagi & Ito, 2021 ). However, it remains to be clarified to what extent providing liquidity on DEXs is advantageous compared to providing liquidity on CEXs or not providing liquidity at all. For this reason, there are already approaches to measure the returns of liquidity providers on DEXs (e.g., Milionis et al., 2023c ). However, most of them are still the subject of open discussion, so there is still room for further approaches to measuring the returns to providing liquidity on DEXs that can be explored in future research.

While adoption of DEXs is gradually increasing, it is important to note that it is evolving at a relatively slow pace. Researchers are actively investigating strategies to accelerate adoption and make DEXs more user-friendly and accessible (Heimbach et al., 2021 ). For many of them, the prevailing shift toward centralization is a major concern (Vidal-Tomás et al., 2023 ). For example, some of them observe a shifting behavior of traders switching between DEXs and CEXs in response to new token listings (Aspris et al., 2021 ) or a trend toward the monopolization of individual CEXs in general (Vidal-Tomás et al., 2023 ). The dominance of a small number of exchanges in handling a significant portion of transactions underscores the importance of exploring mechanisms to maintain a decentralized ecosystem (Sai et al., 2021 ). A significant amount of research focuses on Uniswap as an empirical starting point for DEX research, taking advantage of its position as the leading DEX (e.g., Fritsch, 2021 ; Ghazzawi & Yanovich, 2023 ; Koroļkovs & Kodors, 2022 ; Lo & Medda, 2020 ; Xia et al., 2021 ). The detection and prevention of fraudulent tokens in platforms such as Uniswap and the broader DeFi ecosystem remain areas of active research to improve the security and integrity of these platforms (Trozze et al., 2023 ; Xia et al., 2021 ). CEXs, acting as choke points , can play a critical role in detecting criminal activity within the DeFi/DEX space by enforcing Know Your Customer (KYC) regulations (Caliskan, 2020 ; Trozze et al., 2023 ). However, because not all CEXs comply with the regulatory requirements imposed on them, or deliberately move their operations overseas where there are little to no requirements, CEXs often fall victim to phishing or other cybersecurity attacks, often with catastrophic consequences for their users. As a result, the research community is focusing on developing indicators for CEXs that can predict and prevent insolvency, recognizing the potential impact on users and the overall market. This emphasis on security and compliance is critical to maintaining the integrity of these platforms and reinforces the need for further research in this area.

The presented and identified research focus areas are only a glimpse of possible open research questions and future research directions perceived in the area of CEXs and DEXs. Especially with regard to the dimensions of user experience and technological aspects, there is still a need for optimization, which requires further research. The potential research directions are thus diverse, multi-perspective, and interdisciplinary, leaving ample room for further development.

This paper conducts a comprehensive literature review of CEXs and DEXs to provide a thorough analysis of their respective research dimensions. After identifying definitions and keywords, a framework is systematically constructed and enriched with appropriate superordinate terms to support this endeavor. The analysis reveals a diverse range of current research in this systematic literature review, with notable quantitative and conceptual contributions from different countries. This compilation of research highlights the contemporary relevance of the topic and provides a multifaceted view of the field. Within the dimensions of research on centralized and decentralized cryptocurrency exchanges, the secondary analysis reveals two distinct market models that exhibit significant differences. These distinctions provide valuable insights into the diverse and complex world of crypto exchanges. The formulation of comprehensive definitions in this context provides a strong foundation for future research. Current research trends go beyond the development of pricing functions for CEXs, HEXs, and DEXs. These topics include front-running in decentralized markets, optimizing transaction sequencing, quantifying returns for liquidity providers, and addressing regulatory concerns such as preventing fraudulent tokens and regulating cryptocurrency exchanges.

While this literature review has taken a systematic and comprehensive approach, it is not without limitations. Despite efforts to cast a wide net by including multiple databases and outlets, the possibility of missing noteworthy papers remains. The selection and extraction process, which was guided by specific criteria, nevertheless retained elements of subjectivity. In addition, the quality and relevance of the literature serve as inherent limitations. The constant evolution of the cryptocurrency exchange landscape, combined with the mismatch between the pace of academic research and market operations, could potentially lead to the neglect of inventive methods that have not been subject to academic scrutiny. These aspects underscore the dynamic nature of the cryptocurrency exchange sphere and the urgent need for ongoing research and analysis.

The identified research directions are relevant not only for researchers, but also for practitioners, as they actively contribute to the evolution of CEXs and DEXs through the creation of innovative protocols. Therefore, all the research questions and directions mentioned in this paper can also be seen as an inspiration for practitioners to invent new, innovative protocols that try to address the problems and issues that currently persist in cryptocurrency markets, thereby advancing research in this area as well.

Data Availability

Appendices/Supplementary materials are available on request by e-mailing the corresponding author.

References marked with * are included in the sample

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Chair of Managerial Accounting, Saarland University, Saarbrücken, Germany

Sascha Hägele

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Hägele, S. Centralized exchanges vs. decentralized exchanges in cryptocurrency markets: A systematic literature review. Electron Markets 34 , 33 (2024). https://doi.org/10.1007/s12525-024-00714-2

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Received : 24 December 2023

Accepted : 22 April 2024

Published : 18 May 2024

DOI : https://doi.org/10.1007/s12525-024-00714-2

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