The PRISMA 2020 statement: an updated guideline for reporting systematic reviews — TEI-tagged view

Matthew J PagepersName, Joanne E McKenziepersName, Patrick M BossuytpersName, Isabelle BoutronpersName, Tammy C HoffmannpersName, Cynthia D MulrowpersName, Larissa ShamseerpersName, Jennifer M TetzlaffpersName, Elie A AklpersName, Sue E BrennanpersName, Roger ChoupersName, Julie GlanvillepersName, Jeremy M GrimshawpersName, Asbjørn HróbjartssonpersName, Manoj M LalupersName, Tianjing LipersName, Elizabeth W LoderpersName, Evan Mayo-WilsonpersName, Steve McDonaldpersName, Luke A McGuinnesspersName, Lesley A StewartpersName, James ThomaspersName, Andrea C TriccopersName, Vivian A WelchpersName, Penny WhitingpersName, David MoherpersName (2021date). “The PRISMA 2020 statement: an updated guideline for reporting systematic reviews.” BMJtitle·j.

Object of study — transparentterm, completeterm, and accurateterm reporting of systematic reviewsterm·mth through the updated PRISMA guideline

Research question — how the 2009date PRISMA statement should be updated to reflect methodological, terminological, technological, and publishing changes

Contribution — the PRISMA 2020 statementterm·mth, including a 27-item checklistterm, expanded recommendations, abstract checklist, and revised flow diagramsterm

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The PRISMA 2020 statementterm·mth: an updated guideline for reporting systematic reviewsterm·mth Abstract The Preferred Reporting Items for Systematic reviewsterm·mth and Meta-Analyses (PRISMA) statement, published in 2009date, was designed to help systematic reviewers transparently reportterm why the review was done, what the authors did, and what they found. Over the past decade, advances in systematic reviewterm·def methodology and terminology have necessitated an update to the guideline. The PRISMA 2020 statementterm·mth replaces the 2009date statement and includes new reporting guidanceterm·mth that reflects advances in methods to identify, select, appraise, and synthesise studies. The structure and presentation of the items have been modified to facilitate implementation. In this article, we present the PRISMA 2020date 27-item checklistterm, an expanded checklistterm that details reporting recommendations for each item, the PRISMA 2020 abstract checklistterm, and the revised flow diagramsterm for original and updated reviews.

Systematic reviewsterm·mth serve many critical roles. They can provide syntheses of the state of knowledge in a field, from which future research priorities can be identified; they can address questions that otherwise could not be answered by individual studies; they can identify problems in primary research that should be rectified in future studies; and they can generate or evaluate theories about how or why phenomena occur. Systematic reviewsterm·mth therefore generate various types of knowledge for different users of reviews (such as patients, healthcare providers, researchers, and policy makers). 1 2 To ensure a systematic reviewterm·def is valuable to users, authors should prepare a transparent, complete, and accurate accountterm of why the review was done, what they did (such as how studies were identified and selected) and what they found (such as characteristics of contributing studies and resultsterm of meta-analyses). Up-to-date reporting guidanceterm·mth facilitates authors achieving this. 3 The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009term·mth (hereafter referred to as PRISMA 2009term·mth) 4 5 6 7 8 9 10 is a reporting guidelineterm·mth designed to address poor reporting of systematic reviewsterm·mth. 11 The PRISMA 2009 statementterm·mth comprised a checklist of 27 items recommended for reporting in systematic reviewsterm·mth and an “explanation and elaboration” paper 12 13 14 15 16 providing additional reporting guidanceterm·mth for each item, along with exemplars of reporting. The recommendations have been widely endorsed and adopted, as evidenced by its co-publication in multiple journals, citation in over 60 000 reportsterm (Scopus, August 2020date), endorsement from almost 200 journals and systematic reviewterm·def organisations, and adoption in various disciplines. Evidence from observational studies suggests that use of the PRISMA 2009 statementterm·mth is associated with more complete reportingterm of systematic reviewsterm·mth, 17 18 19 20 although more could be done to improve adherenceterm·var to the guideline. 21 Many innovations in the conduct of systematic reviewsterm·mth have occurred since publication of the PRISMA 2009 statementterm·mth. For example, technological advances have enabled the use of natural language processingterm and machine learningterm to identify relevant evidence, 22 23 24 methods have been proposed to synthesise and present findings when meta-analysisterm is not possible or appropriate, 25 26 27 and new methods have been developed to assess the risk of biasterm in resultsterm of included studies. 28 29 Evidence on sources of bias in systematic reviewsterm·mth has accrued, culminating in the development of new tools to appraise the conduct of systematic reviewsterm·mth. 30 31 Terminology used to describe particular review processes has also evolved, as in the shift from assessing “quality” to assessing “certaintyterm” in the body of evidence. 32 In addition, the publishing landscape has transformed, with multiple avenues now available for registering and disseminating systematic review protocolsterm, 33 34 disseminating reportsterm of systematic reviewsterm·mth, and sharing data and materials, such as preprint serversterm and publicly accessible repositoriesterm. To capture these advances in the reporting of systematic reviewsterm·mth necessitated an update to the PRISMA 2009 statementterm·mth.

To ensure a systematic reviewterm·def is valuable to users, authors should prepare a transparent, complete, and accurate accountterm of why the review was done, what they did, and what they found The PRISMA 2020 statementterm·mth provides updated reporting guidanceterm·mth for systematic reviewsterm·mth that reflects advances in methods to identify, select, appraise, and synthesise studies The PRISMA 2020 statementterm·mth consists of a 27-item checklistterm, an expanded checklistterm that details reporting recommendations for each item, the PRISMA 2020 abstract checklistterm, and revised flow diagramsterm for original and updated reviews We anticipate that the PRISMA 2020 statementterm·mth will benefit authors, editors, and peer reviewers of systematic reviewsterm·mth, and different users of reviews, including guideline developers, policy makers, healthcare providers, patients, and other stakeholders Development of PRISMA 2020date A completeterm description of the methods used to develop PRISMA 2020date is available elsewhere. 35 We identified PRISMA 2009term·mth items that were often reported incompletely by examining the resultsterm of studies investigating the transparency of reportingterm of published reviews. 17 21 36 37 We identified possible modifications to the PRISMA 2009 statementterm·mth by reviewing 60 documents providing reporting guidanceterm·mth for systematic reviewsterm·mth (including reporting guidelinesterm·mth, handbooks, tools, and meta-research studies). 38 These reviews of the literature were used to inform the content of a survey with suggested possible modifications to the 27 items in PRISMA 2009term·mth and possible additional items. Respondents were asked whether they believed we should keep each PRISMA 2009term·mth item as is, modify it, or remove it, and whether we should add each additional item. Systematic review methodologiststerm and journal editorsterm were invited to completeterm the online surveyterm (110 of 220 invited responded). We discussed proposed content and wording of the PRISMA 2020 statementterm·mth, as informed by the review and survey resultsterm, at a 21-member, two-day, in-person meetingterm in September 2018 in Edinburgh, Scotland. Throughout 2019 and 2020date, we circulated an initial draft and five revisions of the checklist and explanation and elaboration paperterm to co-authors for feedback. In April 2020date, we invited 22 systematic reviewers who had expressed interest in providing feedback on the PRISMA 2020 checklistterm to share their views (via an online surveyterm) on the layout and terminology used in a preliminary version of the checklist. Feedback was received from 15 individuals and considered by the first author, and any revisions deemed necessary were incorporated before the final version was approved and endorsed by all co-authors.

The PRISMA 2020 statementterm·mth Scope of the guideline The PRISMA 2020 statementterm·mth has been designed primarily for systematic reviewsterm·mth of studies that evaluate the effects of health interventionsterm, irrespective of the design of the included studies. However, the checklist items are applicable to reportsterm of systematic reviewsterm·mth evaluating other interventions (such as social or educational interventionsterm), and many items are applicable to systematic reviewsterm·mth with objectives other than evaluating interventions (such as evaluating aetiologyterm, prevalenceterm, or prognosisterm). PRISMA 2020date is intended for use in systematic reviewsterm·mth that include synthesis (such as pairwise meta-analysisterm or other statistical synthesisterm·mth methods) or do not include synthesis (for example, because only one eligible studyterm·mth is identified). The PRISMA 2020date items are relevant for mixed-methods systematic reviewsterm·mth (which include quantitative and qualitative studiesterm), but reporting guidelinesterm·mth addressing the presentation and synthesis of qualitative data should also be consulted. 39 40 PRISMA 2020date can be used for original systematic reviewsterm·mth, updated systematic reviewsterm·mth, or continually updated (“living”) systematic reviewsterm·mth. However, for updated and living systematic reviewsterm·mth, there may be some additional considerations that need to be addressed. Where there is relevant content from other reporting guidelinesterm·mth, we reference these guidelines within the items in the explanation and elaboration paperterm 41 (such as PRISMA-Search 42 in items 6 and 7, Synthesis without meta-analysisterm (SWiM) reporting guidelineterm·mth 27 in item 13d). Box 1 includes a glossary of terms used throughout the PRISMA 2020 statementterm·mth.

Systematic reviewterm·def —A review that uses explicit, systematic methods to collate and synthesise findings of studies that address a clearly formulated question 43 Statistical synthesisterm·mth —The combination of quantitative resultsterm of two or more studies. This encompasses meta-analysis of effect estimatesterm·mth (described below) and other methods, such as combining P values, calculating the range and distribution of observed effects, and vote counting based on the direction of effect (see McKenziepersName and BrennanpersName 25 for a description of each method) Meta-analysis of effect estimatesterm·mth —A statistical technique used to synthesise resultsterm when studyterm·mth effect estimates and their variances are available, yielding a quantitative summary of resultsterm 25 Outcometerm —An event or measurement collected for participants in a studyterm·mth (such as quality of life, mortality) Resultterm —The combination of a point estimate (such as a mean difference, risk ratio, or proportion) and a measure of its precision (such as a confidence/credible interval) for a particular outcometerm Reportterm —A document (paper or electronic) supplying information about a particular studyterm·mth. It could be a journal article, preprint, conference abstract, studyterm·mth register entry, clinical studyterm·mth reportterm, dissertation, unpublished manuscript, government reportterm, or any other document providing relevant information Recordterm —The title or abstract (or both) of a reportterm indexed in a database or website (such as a title or abstract for an article indexed in Medline). Recordsterm that refer to the same reportterm (such as the same journal article) are “duplicatesterm”; however, recordsterm that refer to reportsterm that are merely similar (such as a similar abstract submitted to two different conferences) should be considered unique.

Studyterm·mth —An investigation, such as a clinical trial, that includes a defined group of participants and one or more interventions and outcomesterm. A “studyterm·mth” might have multiple reportsterm. For example, reportsterm could include the protocol, statistical analysis plan, baseline characteristics, resultsterm for the primary outcometerm, resultsterm for harms, resultsterm for secondary outcomesterm, and resultsterm for additional mediator and moderator analyses PRISMA 2020date is not intended to guide systematic reviewterm·def conduct, for which comprehensive resources are available. 43 44 45 46 However, familiarity with PRISMA 2020date is useful when planning and conducting systematic reviewsterm·mth to ensure that all recommended information is captured. PRISMA 2020date should not be used to assess the conduct or methodological quality of systematic reviewsterm·mth; other tools exist for this purpose. 30 31 Furthermore, PRISMA 2020date is not intended to inform the reporting of systematic review protocolsterm, for which a separate statement is available (PRISMA for Protocols (PRISMA-P) 2015 statementterm·mth 47 48 ). Finally, extensions to the PRISMA 2009 statementterm·mth have been developed to guide reporting of network meta-analysesterm, 49 meta-analyses of individual participant data, 50 systematic reviewsterm·mth of harms, 51 systematic reviewsterm·mth of diagnostic test accuracy studies, 52 and scoping reviewsterm 53 ; for these types of reviews we recommend authors reportterm their review in accordance with the recommendations in PRISMA 2020date along with the guidance specific to the extension.

How to use PRISMA 2020date The PRISMA 2020 statementterm·mth (including the checklists, explanation and elaboration, and flow diagram) replaces the PRISMA 2009 statementterm·mth, which should no longer be used. Box 2 summarises noteworthy changes from the PRISMA 2009 statementterm·mth. The PRISMA 2020 checklistterm includes seven sectionsterm with 27 items, some of which include sub-items ( table 1 ). A checklist for journal and conference abstracts for systematic reviewsterm·mth is included in PRISMA 2020date. This abstract checklist is an update of the 2013 PRISMA for Abstracts statement, 54 reflecting new and modified content in PRISMA 2020date ( table 2 ). A template PRISMA flow diagram is provided, which can be modified depending on whether the systematic reviewterm·def is original or updated ( fig 1 ).

Inclusion of the abstract reporting checklist within PRISMA 2020date (see item #2 and table 2 ).

Movement of the ‘Protocol and registration’ item from the start of the Methods section of the checklist to a new Other section, with addition of a sub-item recommending authors describe amendments to information provided at registration or in the protocol (see item #24a-24c).

Modification of the ‘Search’ item to recommend authors present full search strategies for all databases, registers and websites searched, not just at least one database (see item #7).

Modification of the ‘Studyterm·mth selection’ item in the Methods section to emphasise the reporting of how many reviewers screened each recordterm and each reportterm retrieved, whether they worked independently, and if applicable, details of automation tools used in the process (see item #8).

Addition of a sub-item to the ‘Data items’ item recommending authors reportterm how outcomesterm were defined, which resultsterm were sought, and methods for selecting a subset of resultsterm from included studies (see item #10a).

Splitting of the ‘Synthesis of resultsterm’ item in the Methods section into six sub-items recommending authors describe: the processes used to decide which studies were eligible for each synthesis; any methods required to prepare the data for synthesis; any methods used to tabulate or visually display resultsterm of individual studies and syntheses; any methods used to synthesise resultsterm; any methods used to explore possible causes of heterogeneityterm·var among studyterm·mth resultsterm (such as subgroup analysis, meta-regression); and any sensitivity analyses used to assess robustnessterm·var of the synthesised resultsterm (see item #13a-13f).

Addition of a sub-item to the ‘Studyterm·mth selection’ item in the Resultsterm section recommending authors cite studies that might appear to meet the inclusion criteria, but which were excluded, and explain why they were excluded (see item #16b).

Splitting of the ‘Synthesis of resultsterm’ item in the Resultsterm section into four sub-items recommending authors: briefly summarise the characteristics and risk of biasterm among studies contributing to the synthesis; present resultsterm of all statistical syntheses conducted; present resultsterm of any investigations of possible causes of heterogeneityterm·var among studyterm·mth resultsterm; and present resultsterm of any sensitivity analyses (see item #20a-20d).

Addition of new items recommending authors reportterm methods for and resultsterm of an assessment of certaintyterm (or confidence) in the body of evidence for an outcometerm (see items #15 and #22).

Addition of a new item recommending authors declare any competing interests (see item #26).

Addition of a new item recommending authors indicate whether data, analytic code and other materials used in the review are publicly available and if so, where they can be found (see item #27).

PRISMA 2020date item checklist PRISMA 2020date for Abstracts checklist* PRISMA 2020date flow diagram template for systematic reviewsterm·mth. The new design is adapted from flow diagrams proposed by Boers, 55 Mayo-WilsonpersName et al. 56 and Stovold et al. 57 The boxes in grey should only be completed if applicable; otherwise they should be removed from the flow diagram. Note that a “reportterm” could be a journal article, preprint, conference abstract, studyterm·mth register entry, clinical studyterm·mth reportterm, dissertation, unpublished manuscript, government reportterm or any other document providing relevant information.

We recommend authors refer to PRISMA 2020date early in the writing process, because prospective consideration of the itemsterm may help to ensure that all the items are addressedterm. To help keep track of which items have been reported, the PRISMA statement website ( http://www.prisma-statement.org/ ) includes fillable templatesterm of the checklists to download and completeterm (also available in the data supplement on bmj.com). We have also created a web applicationterm that allows users to completeterm the checklist via a user-friendly interface 58 (available at https://prisma.shinyapps.io/checklist/ and adapted from the Transparency Checklist app 59 ). The completed checklist can be exported to Word or PDF. Editable templates of the flow diagram can also be downloaded from the PRISMA statement website.

We have prepared an updated explanation and elaboration paperterm, in which we explain why reporting of each item is recommended and present bullet points that detail the reporting recommendations (which we refer to as elements). 41 The bullet-point structure is new to PRISMA 2020date and has been adopted to facilitate implementation of the guidance. 60 61 An expanded checklistterm, which comprises an abridged version of the elements presented in the explanation and elaboration paperterm, with references and some examples removed, is available in the data supplement on bmj.com. Consulting the explanation and elaboration paperterm is recommended if further clarity or information is required.

Journals and publishers might impose word and section limits, and limits on the number of tables and figures allowed in the main reportterm. In such cases, if the relevant information for some items already appears in a publicly accessible review protocol, referring to the protocol may suffice. Alternatively, placing detailed descriptions of the methods used or additional resultsterm (such as for less critical outcomesterm) in supplementary files is recommended. Ideally, supplementary files should be deposited to a general-purpose or institutional open-access repository that provides free and permanent access to the material (such as Open Science Framework, Dryad, figshare). A reference or link to the additional information should be included in the main reportterm. Finally, although PRISMA 2020date provides a template for where information might be located, the suggested location should not be seen as prescriptive; the guiding principle is to ensure the information is reported.

Discussion Use of PRISMA 2020date has the potential to benefit many stakeholders. Complete reportingterm allows readers to assess the appropriateness of the methodsterm, and therefore the trustworthiness of the findings. Presenting and summarising characteristicsterm of studies contributing to a synthesis allows healthcare providers and policy makers to evaluate the applicability of the findingsterm to their setting. Describing the certaintyterm in the body of evidence for an outcometerm and the implications of findings should help policy makers, managers, and other decision makers formulate appropriate recommendationsterm for practice or policy. Complete reporting of all PRISMA 2020 itemsterm also facilitates replication and review updatesterm, as well as inclusion of systematic reviewsterm·mth in overviews (of systematic reviewsterm·mth) and guidelines, so teams can leverage work that is already done and decrease research wasteterm. 36 62 63 We updated the PRISMA 2009 statementterm·mth by adapting the EQUATOR Network’s guidance for developing health research reporting guidelinesterm·mth. 64 We evaluated the reporting completenessterm·var of published systematic reviewsterm·mth, 17 21 36 37 reviewed the items included in other documents providing guidance for systematic reviewsterm·mth, 38 surveyed systematic review methodologiststerm and journal editorsterm for their views on how to revise the original PRISMA statement, 35 discussed the findings at an in-person meetingterm, and prepared this document through an iterative process. Our recommendations are informed by the reviews and survey conducted before the in-person meetingterm, theoretical considerations about which items facilitate replicationterm and help users assess the risk of biasterm and applicabilityterm·var of systematic reviewsterm·mth, and co-authors’ experience with authoring and using systematic reviewsterm·mth.

Various strategies to increase the use of reporting guidelinesterm·mth and improve reporting have been proposed. They include educators introducing reporting guidelinesterm·mth into graduate curricula to promote good reporting habits of early career scientists 65 ; journal editorsterm and regulators endorsing use of reporting guidelinesterm·mth 18 ; peer reviewers evaluating adherenceterm·var to reporting guidelinesterm·mth 61 66 ; journals requiring authors to indicate where in their manuscript they have adhered to each reporting item 67 ; and authors using online writing tools that prompt complete reportingterm at the writing stage. 60 Multi-pronged interventions, where more than one of these strategies are combined, may be more effective (such as completion of checklists coupled with editorial checks). 68 However, of 31 interventions proposed to increase adherenceterm·var to reporting guidelinesterm·mth, the effects of only 11 have been evaluated, mostly in observational studies at high risk of biasterm due to confounding. 69 It is therefore unclear which strategies should be used. Future research might explore barriers and facilitators to the use of PRISMA 2020date by authors, editors, and peer reviewers, designing interventions that address the identified barriers, and evaluating those interventions using randomised trialsterm. To inform possible revisions to the guideline, it would also be valuable to conduct think-aloud studiesterm 70 to understand how systematic reviewers interpret the items, and reliability studiesterm to identify items where there is varied interpretation of the items.

We encourage readers to submit evidence that informs any of the recommendations in PRISMA 2020date (via the PRISMA statement website: http://www.prisma-statement.org/ ). To enhance accessibility of PRISMA 2020date, several translations of the guideline are under way (see available translations at the PRISMA statement website). We encourage journal editorsterm and publishers to raise awareness of PRISMA 2020date (for example, by referring to it in journal “Instructions to authors”), endorsing its use, advising editors and peer reviewers to evaluate submitted systematic reviewsterm·mth against the PRISMA 2020 checkliststerm, and making changes to journal policies to accommodate the new reporting recommendations. We recommend existing PRISMA extensions 47 49 50 51 52 53 71 72 be updated to reflect PRISMA 2020date and advise developers of new PRISMA extensions to use PRISMA 2020date as the foundation document.

Conclusion We anticipate that the PRISMA 2020 statementterm·mth will benefit authors, editors, and peer reviewers of systematic reviewsterm·mth, and different users of reviews, including guideline developers, policy makers, healthcare providers, patients, and other stakeholders. Ultimately, we hope that uptake of the guideline will lead to more transparentterm, completeterm, and accurateterm reporting of systematic reviewsterm·mth, thus facilitating evidence based decision making.