The PRISMA 2020 statement: an updated guideline for reporting systematic reviews

The PRISMA 2020 statement: an updated guideline for reporting systematic reviews Matthew J Page Joanne E McKenzie Patrick M Bossuyt Isabelle Boutron Tammy C Hoffmann Cynthia D Mulrow Larissa Shamseer Jennifer M Tetzlaff Elie A Akl Sue E Brennan Roger Chou Julie Glanville Jeremy M Grimshaw Asbjørn Hróbjartsson Manoj M Lalu Tianjing Li Elizabeth W Loder Evan Mayo-Wilson Steve McDonald Luke A McGuinness Lesley A Stewart James Thomas Andrea C Tricco Vivian A Welch Penny Whiting David Moher

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197 spans located by searching the stored text for the quote's exact words, allowing any whitespace between them transparent, complete, and accurate reporting of systematic reviews through the updated PRISMA guideline how the 2009 PRISMA statement should be updated to reflect methodological, terminological, technological, and publishing changes the PRISMA 2020 statement, including a 27-item checklist, expanded recommendations, abstract checklist, and revised flow diagrams method incomplete systematic-review reporting and the effects of reporting completeness on appraisal, reuse, updating, and decision making expert-consensusexpert-consensus Makes review rationale, procedures, and findings available to users.transparent reporting Adds guidance as evidence-identification, synthesis, and bias-assessment methods evolve.methodological updating Generates candidate modifications and additions to the checklist.guidance-document review Elicits keep, modify, remove, and add judgments for reporting items.stakeholder survey Uses multidisciplinary discussion to refine content and wording.consensus meeting Incorporates co-author and external-reviewer feedback before approval.iterative revision Helps authors capture recommended information during writing.prospective checklist use Let authors track which items have been reported.fillable checklist templates Provide concise implementation detail for each reporting recommendation.bullet-point elements Keeps detailed methods and results accessible when article space is constrained.repository linkage Enables assessment, replication, updating, and downstream synthesis reuse.complete reporting Combine checklist completion with editorial or other checks to improve uptake.multi-pronged interventions Use think-aloud and reliability designs to expose barriers and ambiguous items.future user studies PRISMA 2020 does not guide how systematic reviews should be conducted. PRISMA 2020 should not be used to assess review conduct or methodological quality. A separate PRISMA-P statement is needed for protocol reporting. Mixed-methods reviews should also consult guidance specific to qualitative synthesis. Updated and living reviews can require additional considerations. Specialized review types require PRISMA extension guidance in addition to the core statement. Journal word, section, table, and figure limits can constrain where recommended information is reported. The suggested locations of information in the template are not prescriptive. The 2009 statement still had incomplete adherence despite broad adoption. The effects of most proposed adherence interventions had not been evaluated. Existing intervention evaluations were mostly observational and at high confounding risk. It remained unclear which adherence strategies should be used. Some checklist items may be interpreted variably and require reliability study. published-review transparency studieseliminates: relying only on opinion to identify incomplete PRISMA 2009 items review of 60 guidance documentseliminates: deriving candidate modifications from a single guidance source structured survey of methodologists and journal editorseliminates: unobserved stakeholder judgments about keeping, modifying, removing, or adding items 21-member in-person consensus meetingeliminates: adopting literature and survey suggestions without multidisciplinary wording review initial draft, five co-author revisions, and external user feedbackeliminates: finalizing layout and terminology after a single drafting pass · outcome: held PRISMA 2020 statementPRISMA 2020 statement systematic reviewssystematic reviews reporting guidancereporting guidance new reporting guidancenew reporting guidance 27-item checklist27-item checklist expanded checklistexpanded checklist PRISMA 2020 abstract checklistPRISMA 2020 abstract checklist revised flow diagramsrevised flow diagrams transparenttransparent completecomplete accurateaccurate PRISMA 2009 statementPRISMA 2009 statement The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009 PRISMA 2009PRISMA 2009 reporting guidelinereporting guideline explanation and elaboration paperexplanation and elaboration paper natural language processingnatural language processing machine learningmachine learning meta-analysismeta-analysis risk of biasrisk of bias certaintycertainty systematic review protocolssystematic review protocols preprint serverspreprint servers publicly accessible repositoriespublicly accessible repositories transparency of reportingtransparency of reporting online surveyonline survey Systematic review methodologistsSystematic review methodologists journal editorsjournal editors in-person meetingin-person meeting health interventionshealth interventions social or educational interventionssocial or educational interventions aetiologyaetiology prevalenceprevalence prognosisprognosis pairwise meta-analysispairwise meta-analysis mixed-methods systematic reviewsmixed-methods systematic reviews quantitative and qualitative studiesquantitative and qualitative studies qualitative studiesqualitative studies living systematic reviewsliving systematic reviews Statistical synthesisStatistical synthesis Meta-analysis of effect estimatesMeta-analysis of effect estimates OutcomeOutcome ResultResult ReportReport RecordRecord StudyStudy duplicatesduplicates PRISMA for Protocols (PRISMA-P) 2015 statementPRISMA for Protocols (PRISMA-P) 2015 statement network meta-analysesnetwork meta-analyses scoping reviewsscoping reviews PRISMA 2020 checklistPRISMA 2020 checklist seven sectionsseven sections fillable templatesfillable templates web applicationweb application replicationreplication review updatesreview updates research wasteresearch waste randomised trialsrandomised trials think-aloud studiesthink-aloud studies reliability studiesreliability studies Up-to-date reporting guidanceUp-to-date reporting guidance transparent, complete, and accurate accounttransparent, complete, and accurate account prospective consideration of the itemsprospective consideration of the items all the items are addressedall the items are addressed Complete reportingComplete reporting appropriateness of the methodsappropriateness of the methods Presenting and summarising characteristicsPresenting and summarising characteristics applicability of the findingsapplicability of the findings Describing the certaintyDescribing the certainty appropriate recommendationsappropriate recommendations Complete reporting of all PRISMA 2020 itemsComplete reporting of all PRISMA 2020 items replication and review updatesreplication and review updates PRISMA 2020 statement → PRISMA 2009 statementPRISMA 2020 replaces PRISMA 2009. PRISMA 2009 statement use → more complete reportingUse of PRISMA 2009 is associated with more complete reporting. quality → certaintyReview terminology shifted from quality to certainty. PRISMA 2020 → systematic review conductPRISMA 2020 is not intended to guide review conduct. PRISMA 2020 → methodological quality assessmentPRISMA 2020 should not assess methodological quality. PRISMA-P 2015 → systematic review protocolsPRISMA-P is the separate statement for protocol reporting. PRISMA extensions → specialized review typesExtensions provide additional guidance for specialized review types. records → reportsMultiple records can refer to one report. studies → reportsOne study can have multiple reports. publicly accessible review protocol → main report informationA public protocol may supply information omitted from the main report. multi-pronged interventions → single strategiesMulti-pronged interventions may be more effective. adherence strategies → guideline useIt is unclear which adherence strategies should be used. journal limits → report placementJournal space limits constrain where information can be reported. existing intervention evaluations → confoundingMost evaluations were observational and at high risk of bias due to confounding. PRISMA as reporting guidance rather than a conduct manual systematic review as explicit question-driven collation and synthesis report as a document and record as its indexed title or abstract study as an investigation that may generate multiple reports result as estimate plus precision rather than an outcome alone certainty as the evolved term replacing quality of an evidence body complete reporting as infrastructure for appraisal and reuse PRISMA 2020 as core guidance supplemented by specialized extensions guideline development as empirical review, consultation, consensus, and iteration guideline uptake as an intervention problem with limited comparative evidence replaces → PRISMA 2009 statementnote: The article explicitly supersedes the earlier reporting statement. extends → reporting guidance for systematic reviewsnote: The update adds new and modified guidance and artifacts. supports → prospective use of reporting checklistsnote: Early checklist use may help authors capture every item. qualifies → PRISMA 2020 as a conduct or quality-assessment toolnote: The stated scope excludes conduct guidance and methodological-quality appraisal. supports → future experimental evaluation of adherence strategiesnote: The article proposes randomized trials because current intervention evidence is limited. PRISMA 2009 statement —is-a→ reporting guidelinethe relation itself is separately evidenced · strength of the relation: 1 · note: Direct categorical class statement. · the relation stated: The PRISMA 2009 statement is a reporting guideline.PRISMA 2009 statementreporting guideline The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009 —same-as→ PRISMA 2009the relation itself is separately evidenced · strength of the relation: 1 · note: Explicit controlled alternative name. · the relation stated: The statement published in 2009 is hereafter referred to as PRISMA 2009.The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009PRISMA 2009 new reporting guidance —part-of→ PRISMA 2020 statementthe relation itself is separately evidenced · strength of the relation: 1 · note: Categorical inclusion. · the relation stated: The PRISMA 2020 statement includes new reporting guidance.new reporting guidancePRISMA 2020 statement 27-item checklist —part-of→ PRISMA 2020 statementthe relation itself is separately evidenced · strength of the relation: 1 · note: Categorical component membership. · the relation stated: The PRISMA 2020 statement consists of a 27-item checklist.27-item checklistPRISMA 2020 statement expanded checklist —part-of→ PRISMA 2020 statementthe relation itself is separately evidenced · strength of the relation: 1 · note: Categorical component membership. · the relation stated: The PRISMA 2020 statement consists of an expanded checklist.expanded checklistPRISMA 2020 statement PRISMA 2020 abstract checklist —part-of→ PRISMA 2020 statementthe relation itself is separately evidenced · strength of the relation: 1 · note: Categorical component membership. · the relation stated: The PRISMA 2020 statement consists of the PRISMA 2020 abstract checklist.PRISMA 2020 abstract checklistPRISMA 2020 statement revised flow diagrams —part-of→ PRISMA 2020 statementthe relation itself is separately evidenced · strength of the relation: 1 · note: Categorical component membership. · the relation stated: The PRISMA 2020 statement consists of revised flow diagrams.revised flow diagramsPRISMA 2020 statement seven sections —part-of→ PRISMA 2020 checklistthe relation itself is separately evidenced · strength of the relation: 1 · note: Categorical checklist structure. · the relation stated: The PRISMA 2020 checklist includes seven sections.seven sectionsPRISMA 2020 checklist quantitative and qualitative studies —part-of→ mixed-methods systematic reviewsthe relation itself is separately evidenced · strength of the relation: 1 · note: Categorical study-type membership. · the relation stated: Mixed-methods systematic reviews include quantitative and qualitative studies.quantitative and qualitative studiesmixed-methods systematic reviews Up-to-date reporting guidance —causes→ transparent, complete, and accurate accountthe relation itself is separately evidenced · strength of the relation: 0.95 · note: Flat positive facilitation claim. · the relation stated: Up-to-date reporting guidance facilitates authors achieving transparent, complete, and accurate reporting.Up-to-date reporting guidancetransparent, complete, and accurate account prospective consideration of the items —causes→ all the items are addressedthe relation itself is separately evidenced · strength of the relation: 0.6 — the record marks this weak · note: Modal positive facilitation claim. · the relation stated: Prospective consideration of the items may help to ensure that all items are addressed. Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but the span says prospective consideration MAY help ensure all items are addressed; hedged.prospective consideration of the itemsall the items are addressed Describing the certainty —causes→ appropriate recommendationsthe relation itself is separately evidenced · strength of the relation: 0.65 — the record marks this weak · note: Normative modal positive claim. · the relation stated: Describing certainty should help decision makers formulate appropriate recommendations. Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but the span says describing certainty SHOULD help decision makers formulate recommendations; hedged.Describing the certaintyappropriate recommendations Complete reporting of all PRISMA 2020 items —causes→ replication and review updatesthe relation itself is separately evidenced · strength of the relation: 0.95 · note: Flat positive facilitation claim. · the relation stated: Complete reporting facilitates replication and review updates.Complete reporting of all PRISMA 2020 itemsreplication and review updates PRISMA 2020 replaces the 2009 statement and reflects advances in evidence identification, selection, appraisal, and synthesis. The updated statement presents a 27-item checklist, expanded recommendations, an abstract checklist, and revised flow diagrams. Systematic reviews can synthesize knowledge, set research priorities, expose primary-study problems, and develop or evaluate theories. PRISMA 2009 was widely endorsed and its use was associated with more complete review reporting. Review methodology, terminology, bias assessment, registration, dissemination, and material-sharing practices changed after 2009. PRISMA 2020 applies beyond health interventions to several other intervention and non-intervention objectives. The guideline applies to reviews with or without statistical synthesis and to original, updated, and living reviews. PRISMA 2020 is not a guide to review conduct or a tool for assessing methodological quality. The PRISMA 2020 checklist has seven sections and 27 items, some with sub-items. The search item now requests full strategies for all searched databases, registers, and websites. Study-selection reporting now covers reviewer counts, independence, and automation tools. Synthesis methods are split into six reporting sub-items spanning eligibility, preparation, display, synthesis, heterogeneity, and sensitivity analysis. New items cover certainty assessment, competing interests, and availability of data, code, and materials. Complete reporting supports appraisal, applicability judgments, replication, updating, overview inclusion, and guideline development. Only 11 of 31 proposed interventions to improve guideline adherence had been evaluated, mostly with confounding-prone observational studies. The authors identify randomized, think-aloud, and reliability studies as priorities for future evaluation. a review using explicit systematic methods to collate and synthesize studies addressing a formulated questionSystematic review combination of quantitative results from at least two studiesStatistical synthesis statistical synthesis using effect estimates and their variances to yield a quantitative summaryMeta-analysis of effect estimates an event or measurement collected for study participantsOutcome a point estimate combined with a measure of precision for an outcomeResult a paper or electronic document supplying information about a studyReport the title, abstract, or both of a report indexed in a database or websiteRecord an investigation with a defined participant group and one or more interventions and outcomesStudy records that refer to the same reportduplicates continually updated systematic reviewsliving systematic reviews 27 — items in both the PRISMA 2009 and PRISMA 2020 core checklists over 60 000 — reports citing PRISMA 2009 in Scopus by August 2020 almost 200 — journals and systematic-review organizations endorsing PRISMA 2009 60 — guidance documents reviewed to identify possible statement modifications 110 of 220 — invited methodologists and editors responding to the development survey 21-member — size of the in-person consensus meeting two-day — duration of the in-person consensus meeting five — checklist and elaboration-paper revisions circulated after the initial draft 15 — reviewers providing feedback on layout and terminology seven — sections in the PRISMA 2020 checklist six — sub-items for reporting synthesis methods 11 — evaluated interventions among 31 proposed adherence interventions transparency of reportingtransparency of reporting reporting completenessreporting completeness risk of biasrisk of bias certaintycertainty heterogeneityheterogeneity robustnessrobustness applicabilityapplicability adherenceadherence

The PRISMA 2020 statement: an updated guideline for reporting systematic reviews

Abstract

The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement, published in 2009, was designed to help systematic reviewers transparently report why the review was done, what the authors did, and what they found. Over the past decade, advances in systematic review methodology and terminology have necessitated an update to the guideline. The PRISMA 2020 statement replaces the 2009 statement and includes new reporting guidance 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 2020 27-item checklist, an expanded checklist that details reporting recommendations for each item, the PRISMA 2020 abstract checklist, and the revised flow diagrams for original and updated reviews.

Systematic reviews 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 reviews 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 review is valuable to users, authors should prepare a transparent, complete, and accurate account 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 results of meta-analyses). Up-to-date reporting guidance facilitates authors achieving this. 3

The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009 (hereafter referred to as PRISMA 2009) 4 5 6 7 8 9 10 is a reporting guideline designed to address poor reporting of systematic reviews. 11 The PRISMA 2009 statement comprised a checklist of 27 items recommended for reporting in systematic reviews and an “explanation and elaboration” paper 12 13 14 15 16 providing additional reporting guidance 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 reports (Scopus, August 2020), endorsement from almost 200 journals and systematic review organisations, and adoption in various disciplines. Evidence from observational studies suggests that use of the PRISMA 2009 statement is associated with more complete reporting of systematic reviews, 17 18 19 20 although more could be done to improve adherence to the guideline. 21

Many innovations in the conduct of systematic reviews have occurred since publication of the PRISMA 2009 statement. For example, technological advances have enabled the use of natural language processing and machine learning to identify relevant evidence, 22 23 24 methods have been proposed to synthesise and present findings when meta-analysis is not possible or appropriate, 25 26 27 and new methods have been developed to assess the risk of bias in results of included studies. 28 29 Evidence on sources of bias in systematic reviews has accrued, culminating in the development of new tools to appraise the conduct of systematic reviews. 30 31 Terminology used to describe particular review processes has also evolved, as in the shift from assessing “quality” to assessing “certainty” in the body of evidence. 32 In addition, the publishing landscape has transformed, with multiple avenues now available for registering and disseminating systematic review protocols, 33 34 disseminating reports of systematic reviews, and sharing data and materials, such as preprint servers and publicly accessible repositories. To capture these advances in the reporting of systematic reviews necessitated an update to the PRISMA 2009 statement.

To ensure a systematic review is valuable to users, authors should prepare a transparent, complete, and accurate account of why the review was done, what they did, and what they found

The PRISMA 2020 statement provides updated reporting guidance for systematic reviews that reflects advances in methods to identify, select, appraise, and synthesise studies

The PRISMA 2020 statement consists of a 27-item checklist, an expanded checklist that details reporting recommendations for each item, the PRISMA 2020 abstract checklist, and revised flow diagrams for original and updated reviews

Development of PRISMA 2020

A complete description of the methods used to develop PRISMA 2020 is available elsewhere. 35 We identified PRISMA 2009 items that were often reported incompletely by examining the results of studies investigating the transparency of reporting of published reviews. 17 21 36 37 We identified possible modifications to the PRISMA 2009 statement by reviewing 60 documents providing reporting guidance for systematic reviews (including reporting guidelines, 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 2009 and possible additional items. Respondents were asked whether they believed we should keep each PRISMA 2009 item as is, modify it, or remove it, and whether we should add each additional item. Systematic review methodologists and journal editors were invited to complete the online survey (110 of 220 invited responded). We discussed proposed content and wording of the PRISMA 2020 statement, as informed by the review and survey results, at a 21-member, two-day, in-person meeting in September 2018 in Edinburgh, Scotland. Throughout 2019 and 2020, we circulated an initial draft and five revisions of the checklist and explanation and elaboration paper to co-authors for feedback. In April 2020, we invited 22 systematic reviewers who had expressed interest in providing feedback on the PRISMA 2020 checklist to share their views (via an online survey) 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 statement

Scope of the guideline

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

Systematic review —A review that uses explicit, systematic methods to collate and synthesise findings of studies that address a clearly formulated question 43

Statistical synthesis —The combination of quantitative results of two or more studies. This encompasses meta-analysis of effect estimates (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 McKenzie and Brennan 25 for a description of each method)

Meta-analysis of effect estimates —A statistical technique used to synthesise results when study effect estimates and their variances are available, yielding a quantitative summary of results 25

Outcome —An event or measurement collected for participants in a study (such as quality of life, mortality)

Result —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 outcome

Report —A document (paper or electronic) supplying information about a particular study. It could be a journal article, preprint, conference abstract, study register entry, clinical study report, dissertation, unpublished manuscript, government report, or any other document providing relevant information

Record —The title or abstract (or both) of a report indexed in a database or website (such as a title or abstract for an article indexed in Medline). Records that refer to the same report (such as the same journal article) are “duplicates”; however, records that refer to reports that are merely similar (such as a similar abstract submitted to two different conferences) should be considered unique.

Study —An investigation, such as a clinical trial, that includes a defined group of participants and one or more interventions and outcomes. A “study” might have multiple reports. For example, reports could include the protocol, statistical analysis plan, baseline characteristics, results for the primary outcome, results for harms, results for secondary outcomes, and results for additional mediator and moderator analyses

PRISMA 2020 is not intended to guide systematic review conduct, for which comprehensive resources are available. 43 44 45 46 However, familiarity with PRISMA 2020 is useful when planning and conducting systematic reviews to ensure that all recommended information is captured. PRISMA 2020 should not be used to assess the conduct or methodological quality of systematic reviews; other tools exist for this purpose. 30 31 Furthermore, PRISMA 2020 is not intended to inform the reporting of systematic review protocols, for which a separate statement is available (PRISMA for Protocols (PRISMA-P) 2015 statement 47 48 ). Finally, extensions to the PRISMA 2009 statement have been developed to guide reporting of network meta-analyses, 49 meta-analyses of individual participant data, 50 systematic reviews of harms, 51 systematic reviews of diagnostic test accuracy studies, 52 and scoping reviews 53 ; for these types of reviews we recommend authors report their review in accordance with the recommendations in PRISMA 2020 along with the guidance specific to the extension.

How to use PRISMA 2020

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

Inclusion of the abstract reporting checklist within PRISMA 2020 (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 ‘Study selection’ item in the Methods section to emphasise the reporting of how many reviewers screened each record and each report 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 report how outcomes were defined, which results were sought, and methods for selecting a subset of results from included studies (see item #10a).

Splitting of the ‘Synthesis of results’ 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 results of individual studies and syntheses; any methods used to synthesise results; any methods used to explore possible causes of heterogeneity among study results (such as subgroup analysis, meta-regression); and any sensitivity analyses used to assess robustness of the synthesised results (see item #13a-13f).

Addition of a sub-item to the ‘Study selection’ item in the Results 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 results’ item in the Results section into four sub-items recommending authors: briefly summarise the characteristics and risk of bias among studies contributing to the synthesis; present results of all statistical syntheses conducted; present results of any investigations of possible causes of heterogeneity among study results; and present results of any sensitivity analyses (see item #20a-20d).

Addition of new items recommending authors report methods for and results of an assessment of certainty (or confidence) in the body of evidence for an outcome (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 2020 item checklist

PRISMA 2020 for Abstracts checklist*

PRISMA 2020 flow diagram template for systematic reviews. The new design is adapted from flow diagrams proposed by Boers, 55 Mayo-Wilson 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 “report” could be a journal article, preprint, conference abstract, study register entry, clinical study report, dissertation, unpublished manuscript, government report or any other document providing relevant information.

We recommend authors refer to PRISMA 2020 early in the writing process, because prospective consideration of the items may help to ensure that all the items are addressed. To help keep track of which items have been reported, the PRISMA statement website ( http://www.prisma-statement.org/ ) includes fillable templates of the checklists to download and complete (also available in the data supplement on bmj.com). We have also created a web application that allows users to complete 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 paper, 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 2020 and has been adopted to facilitate implementation of the guidance. 60 61 An expanded checklist, which comprises an abridged version of the elements presented in the explanation and elaboration paper, with references and some examples removed, is available in the data supplement on bmj.com. Consulting the explanation and elaboration paper 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 report. 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 results (such as for less critical outcomes) 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 report. Finally, although PRISMA 2020 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 2020 has the potential to benefit many stakeholders. Complete reporting allows readers to assess the appropriateness of the methods, and therefore the trustworthiness of the findings. Presenting and summarising characteristics of studies contributing to a synthesis allows healthcare providers and policy makers to evaluate the applicability of the findings to their setting. Describing the certainty in the body of evidence for an outcome and the implications of findings should help policy makers, managers, and other decision makers formulate appropriate recommendations for practice or policy. Complete reporting of all PRISMA 2020 items also facilitates replication and review updates, as well as inclusion of systematic reviews in overviews (of systematic reviews) and guidelines, so teams can leverage work that is already done and decrease research waste. 36 62 63

We updated the PRISMA 2009 statement by adapting the EQUATOR Network’s guidance for developing health research reporting guidelines. 64 We evaluated the reporting completeness of published systematic reviews, 17 21 36 37 reviewed the items included in other documents providing guidance for systematic reviews, 38 surveyed systematic review methodologists and journal editors for their views on how to revise the original PRISMA statement, 35 discussed the findings at an in-person meeting, and prepared this document through an iterative process. Our recommendations are informed by the reviews and survey conducted before the in-person meeting, theoretical considerations about which items facilitate replication and help users assess the risk of bias and applicability of systematic reviews, and co-authors’ experience with authoring and using systematic reviews.

Various strategies to increase the use of reporting guidelines and improve reporting have been proposed. They include educators introducing reporting guidelines into graduate curricula to promote good reporting habits of early career scientists 65 ; journal editors and regulators endorsing use of reporting guidelines 18 ; peer reviewers evaluating adherence to reporting guidelines 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 reporting 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 adherence to reporting guidelines, the effects of only 11 have been evaluated, mostly in observational studies at high risk of bias 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 2020 by authors, editors, and peer reviewers, designing interventions that address the identified barriers, and evaluating those interventions using randomised trials. To inform possible revisions to the guideline, it would also be valuable to conduct think-aloud studies 70 to understand how systematic reviewers interpret the items, and reliability studies 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 2020 (via the PRISMA statement website: http://www.prisma-statement.org/ ). To enhance accessibility of PRISMA 2020, several translations of the guideline are under way (see available translations at the PRISMA statement website). We encourage journal editors and publishers to raise awareness of PRISMA 2020 (for example, by referring to it in journal “Instructions to authors”), endorsing its use, advising editors and peer reviewers to evaluate submitted systematic reviews against the PRISMA 2020 checklists, 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 2020 and advise developers of new PRISMA extensions to use PRISMA 2020 as the foundation document.

Conclusion

We anticipate that the PRISMA 2020 statement will benefit authors, editors, and peer reviewers of systematic reviews, 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 transparent, complete, and accurate reporting of systematic reviews, thus facilitating evidence based decision making.