Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA StatementFREE
Editor's Note: In order to encourage dissemination of the PRISMA Statement, this article is freely accessible on the Annals of Internal Medicine Web site (www.annals.org) and will be also published in PLOS Medicine, BMJ, Journal of Clinical Epidemiology, and Open Medicine. The authors jointly hold the copyright of this article. For details on further use, see the PRISMA Web site (www.prisma-statement.org).
Systematic reviews and meta-analyses have become increasingly important in health care. Clinicians read them to keep up to date with their field (1, 2), and they are often used as a starting point for developing clinical practice guidelines. Granting agencies may require a systematic review to ensure there is justification for further research (3), and some health care journals are moving in this direction (4). As with all research, the value of a systematic review depends on what was done, what was found, and the clarity of reporting. As with other publications, the reporting quality of systematic reviews varies, limiting readers' ability to assess the strengths and weaknesses of those reviews.
Several early studies evaluated the quality of review reports. In 1987, Mulrow examined 50 review articles published in four leading medical journals in 1985 and 1986 and found that none met all eight explicit scientific criteria, such as a quality assessment of included studies (5). In 1987, Sacks and colleagues (6) evaluated the adequacy of reporting of 83 meta-analyses on 23 characteristics in six domains. Reporting was generally poor; between one and 14 characteristics were adequately reported (mean = 7.7; standard deviation = 2.7). A 1996 update of this study found little improvement (7).
In 1996, to address the suboptimal reporting of meta-analyses, an international group developed a guidance called the QUOROM Statement (QUality Of Reporting Of Meta-analyses), which focused on the reporting of meta-analyses of randomized, controlled trials (8). In this article, we summarize a revision of these guidelines, renamed PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses), which have been updated to address several conceptual and practical advances in the science of systematic reviews (Box 1).
The terminology used to describe a systematic review and meta-analysis has evolved over time. One reason for changing the name from QUOROM to PRISMA was the desire to encompass both systematic reviews and meta-analyses. We have adopted the definitions used by the Cochrane Collaboration (9). A systematic review is a review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyze data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyze and summarize the results of the included studies. Meta-analysis refers to the use of statistical techniques in a systematic review to integrate the results of included studies.
Developing the PRISMA Statement
A three-day meeting was held in Ottawa, Ontario, Canada, in June 2005 with 29 participants, including review authors, methodologists, clinicians, medical editors, and a consumer. The objective of the Ottawa meeting was to revise and expand the QUOROM checklist and flow diagram, as needed.
The executive committee completed the following tasks, prior to the meeting: a systematic review of studies examining the quality of reporting of systematic reviews, and a comprehensive literature search to identify methodological and other articles that might inform the meeting, especially in relation to modifying checklist items. An international survey of review authors, consumers, and groups commissioning or using systematic reviews and meta-analyses was completed, including the International Network of Agencies for Health Technology Assessment (INAHTA) and the Guidelines International Network (GIN). The survey aimed to ascertain views of QUOROM, including the merits of the existing checklist items. The results of these activities were presented during the meeting and are summarized on the PRISMA Web site (www.prisma-statement.org).
Only items deemed essential were retained or added to the checklist. Some additional items are nevertheless desirable, and review authors should include these, if relevant (10). For example, it is useful to indicate whether the systematic review is an update (11) of a previous review, and to describe any changes in procedures from those described in the original protocol.
Shortly after the meeting a draft of the PRISMA checklist was circulated to the group, including those invited to the meeting but unable to attend. A disposition file was created containing comments and revisions from each respondent, and the checklist was subsequently revised 11 times. The group approved the checklist, flow diagram, and this summary paper.
Although no direct evidence was found to support retaining or adding some items, evidence from other domains was believed to be relevant. For example, Item 5 asks authors to provide registration information about the systematic review, including a registration number, if available. Although systematic review registration is not yet widely available (12, 13), the participating journals of the International Committee of Medical Journal Editors (ICMJE) (14) now require all clinical trials to be registered in an effort to increase transparency and accountability (15). Those aspects are also likely to benefit systematic reviewers, possibly reducing the risk of an excessive number of reviews addressing the same question (16, 17) and providing greater transparency when updating systematic reviews.
The PRISMA Statement
The PRISMA Statement consists of a 27-item checklist (Table 1; see also Table S1, for a downloadable Word template for researchers to re-use) and a four-phase flow diagram (Figure 1; see also Figure S1, for a downloadable Word template for researchers to re-use). The aim of the PRISMA Statement is to help authors improve the reporting of systematic reviews and meta-analyses. We have focused on randomized trials, but PRISMA can also be used as a basis for reporting systematic reviews of other types of research, particularly evaluations of interventions. PRISMA may also be useful for critical appraisal of published systematic reviews. However, the PRISMA checklist is not a quality assessment instrument to gauge the quality of a systematic review.
From QUOROM to PRISMA
The new PRISMA checklist differs in several respects from the QUOROM checklist, and the substantive specific changes are highlighted in Table 2. Generally, the PRISMA checklist “decouples” several items present in the QUOROM checklist and, where applicable, several checklist items are linked to improve consistency across the systematic review report.
The flow diagram has also been modified. Before including studies and providing reasons for excluding others, the review team must first search the literature. This search results in records. Once these records have been screened and eligibility criteria applied, a smaller number of articles will remain. The number of included articles might be smaller (or larger) than the number of studies, because articles may report on multiple studies and results from a particular study may be published in several articles. To capture this information, the PRISMA flow diagram now requests information on these phases of the review process.
The PRISMA Statement should replace the QUOROM Statement for those journals that have endorsed QUOROM. We hope that other journals will support PRISMA; they can do so by registering on the PRISMA Web site. To underscore to authors, and others, the importance of transparent reporting of systematic reviews, we encourage supporting journals to reference the PRISMA Statement and include the PRISMA Web address in their instructions to authors. We also invite editorial organizations to consider endorsing PRISMA and encourage authors to adhere to its principles.
The PRISMA Explanation and Elaboration Paper
In addition to the PRISMA Statement, a supporting Explanation and Elaboration document has been produced (18) following the style used for other reporting guidelines (19–21). The process of completing this document included developing a large database of exemplars to highlight how best to report each checklist item, and identifying a comprehensive evidence base to support the inclusion of each checklist item. The Explanation and Elaboration document was completed after several face-to-face meetings and numerous iterations among several meeting participants, after which it was shared with the whole group for additional revisions and final approval. Finally, the group formed a dissemination subcommittee to help disseminate and implement PRISMA.
The quality of reporting of systematic reviews is still not optimal (22–27). In a recent review of 300 systematic reviews, few authors reported assessing possible publication bias (22), even though there is overwhelming evidence both for its existence (28) and its impact on the results of systematic reviews (29). Even when the possibility of publication bias is assessed, there is no guarantee that systematic reviewers have assessed or interpreted it appropriately (30). Although the absence of reporting such an assessment does not necessarily indicate that it was not done, reporting an assessment of possible publication bias is likely to be a marker of the thoroughness of the conduct of the systematic review.
Several approaches have been developed to conduct systematic reviews on a broader array of questions. For example, systematic reviews are now conducted to investigate cost-effectiveness (31), diagnostic (32) or prognostic questions (33), genetic associations (34), and policy making (35). The general concepts and topics covered by PRISMA are all relevant to any systematic review, not just those whose objective is to summarize the benefits and harms of a health care intervention. However, some modifications of the checklist items or flow diagram will be necessary in particular circumstances. For example, assessing the risk of bias is a key concept, but the items used to assess this in a diagnostic review are likely to focus on issues such as the spectrum of patients and the verification of disease status, which differ from reviews of interventions. The flow diagram will also need adjustments when reporting individual patient data meta-analysis (36).
We have developed an explanatory document (18) to increase the usefulness of PRISMA. For each checklist item, this document contains an example of good reporting, a rationale for its inclusion, and supporting evidence, including references, whenever possible. We believe this document will also serve as a useful resource for those teaching systematic review methodology. We encourage journals to include reference to the explanatory document in their Instructions to Authors.
Like any evidence-based endeavor, PRISMA is a living document. To this end we invite readers to comment on the revised version, particularly the new checklist and flow diagram, through the PRISMA Web site. We will use such information to inform PRISMA's continued development.
Oxman AD, Cook DJ, Guyatt GH. Users' guides to the medical literature. VI. How to use an overview. Evidence-Based Medicine Working Group. JAMA. 1994;272:1367-71. [PMID: 7933399] CrossrefMedlineGoogle Scholar
Swingler GH, Volmink J, Ioannidis JP. Number of published systematic reviews and global burden of disease: database analysis. BMJ. 2003;327:1083-4. [PMID: 14604930] CrossrefMedlineGoogle Scholar
- 3. Canadian Institutes of Health Research. Randomized controlled trials registration/application checklist. December 2006. Accessed at www.cihr-irsc.gc.ca/e/documents/rct_reg_e.pdf on 19 May 2009. Google Scholar
Young C, Horton R. Putting clinical trials into context. Lancet. 2005;366:107-8. [PMID: 16005318] CrossrefMedlineGoogle Scholar
Mulrow CD. The medical review article: state of the science. Ann Intern Med. 1987;106:485-8. [PMID: 3813259] LinkGoogle Scholar
Sacks HS, Berrier J, Reitman D, Ancona-Berk VA, Chalmers TC. Meta-analyses of randomized controlled trials. N Engl J Med. 1987;316:450-5. [PMID: 3807986] CrossrefMedlineGoogle Scholar
Sacks HS, Reitman D, Pagano D, Kupelnick B. Meta-analysis: an update. Mt Sinai J Med. 1996;63:216-24. [PMID: 8692168] MedlineGoogle Scholar
Moher D, Cook DJ, Eastwood S, Olkin I, Rennie D, Stroup DF. Improving the quality of reports of meta-analyses of randomised controlled trials: the QUOROM statement. Quality of Reporting of Meta-analyses. Lancet. 1999;354:1896-900. [PMID: 10584742] CrossrefMedlineGoogle Scholar
- 9. Green S, Higgins J, eds. Glossary. In: Cochrane Handbook for Systematic Reviews of Interventions 4.2.5. The Cochrane Collaboration; 2005. Accessed at www.cochrane.org/resources/glossary.htm on 19 May 2009. Google Scholar
Strech D, Tilburt J. Value judgments in the analysis and synthesis of evidence. J Clin Epidemiol. 2008;61:521-4. [PMID: 18471654] CrossrefMedlineGoogle Scholar
Moher D, Tsertsvadze A. Systematic reviews: when is an update an update? Lancet. 2006;367:881-3. [PMID: 16546523] CrossrefMedlineGoogle Scholar
- 12. University of York Centre for Reviews and Dissemination. 2009. Accessed at www.york.ac.uk/inst/crd/ on 19 May 2009. Google Scholar
- 13. The Joanna Briggs Institute protocols & work in progress. 2009. Accessed at www.joannabriggs.edu.au/pubs/systematic_reviews_prot.php on 19 May 2009. Google Scholar
De Angelis C, Drazen JM, Frizelle FA, Haug C, Hoey J, Horton R, et al; International Committee of Medical Journal Editors. Clinical trial registration: a statement from the International Committee of Medical Journal Editors [Editorial]. CMAJ. 2004;171:606-7. [PMID: 15367465] CrossrefMedlineGoogle Scholar
Whittington CJ, Kendall T, Fonagy P, Cottrell D, Cotgrove A, Boddington E. Selective serotonin reuptake inhibitors in childhood depression: systematic review of published versus unpublished data. Lancet. 2004;363:1341-5. [PMID: 15110490] CrossrefMedlineGoogle Scholar
Bagshaw SM, McAlister FA, Manns BJ, Ghali WA. Acetylcysteine in the prevention of contrast-induced nephropathy: a case study of the pitfalls in the evolution of evidence. Arch Intern Med. 2006;166:161-6. [PMID: 16432083] CrossrefMedlineGoogle Scholar
Biondi-Zoccai GG, Lotrionte M, Abbate A, Testa L, Remigi E, Burzotta F, et al. Compliance with QUOROM and quality of reporting of overlapping meta-analyses on the role of acetylcysteine in the prevention of contrast associated nephropathy: case study. BMJ. 2006;332:202-9. [PMID: 16415336] CrossrefMedlineGoogle Scholar
Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche P, Ioannidis JP, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. Ann Intern Med. 2009;151:W-65-94. LinkGoogle Scholar
Altman DG, Schulz KF, Moher D, Egger M, Davidoff F, Elbourne D, et al; CONSORT GROUP (Consolidated Standards of Reporting Trials). The revised CONSORT statement for reporting randomized trials: explanation and elaboration. Ann Intern Med. 2001;134:663-94. [PMID: 11304107] LinkGoogle Scholar
Bossuyt PM, Reitsma JB, Bruns DE, Gatsonis CA, Glasziou PP, Irwig LM, et al; Standards for Reporting of Diagnostic Accuracy. The STARD statement for reporting studies of diagnostic accuracy: explanation and elaboration. Ann Intern Med. 2003;138:W1-12. [PMID: 12513067] LinkGoogle Scholar
Vandenbroucke JP, von Elm E, Altman DG, Gøtzsche PC, Mulrow CD, Pocock SJ, et al; STROBE Initiative. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. Ann Intern Med. 2007;147:W163-94. [PMID: 17938389] LinkGoogle Scholar
Moher D, Tetzlaff J, Tricco AC, Sampson M, Altman DG. Epidemiology and reporting characteristics of systematic reviews. PLoS Med. 2007;4:78. [PMID: 17388659] CrossrefMedlineGoogle Scholar
Bhandari M, Morrow F, Kulkarni AV, Tornetta P. Meta-analyses in orthopaedic surgery. A systematic review of their methodologies. J Bone Joint Surg Am. 2001;83-A:15-24. [PMID: 11205853] CrossrefMedlineGoogle Scholar
Kelly KD, Travers A, Dorgan M, Slater L, Rowe BH. Evaluating the quality of systematic reviews in the emergency medicine literature. Ann Emerg Med. 2001;38:518-26. [PMID: 11679863] CrossrefMedlineGoogle Scholar
Richards D. The quality of systematic reviews in dentistry. Evid Based Dent. 2004;5:17. [PMID: 15238972] CrossrefMedlineGoogle Scholar
Choi PT, Halpern SH, Malik N, Jadad AR, Tramèr MR, Walder B. Examining the evidence in anesthesia literature: a critical appraisal of systematic reviews. Anesth Analg. 2001;92:700-9. [PMID: 11226105] CrossrefMedlineGoogle Scholar
Delaney A, Bagshaw SM, Ferland A, Manns B, Laupland KB, Doig CJ. A systematic evaluation of the quality of meta-analyses in the critical care literature. Crit Care. 2005;9:R575-82. [PMID: 16277721] CrossrefMedlineGoogle Scholar
Dickersin K. Publication bias: recognizing the problem, understanding its origins and scope, and preventing harm.. In: Rothstein HR, Sutton AJ, Borenstein M, eds. Publication Bias in Meta-Analysis—Prevention, Assessment and Adjustments. Chichester, UK: J Wiley; 2005:11-33. Google Scholar
Sutton AJ. Evidence concerning the consequences of publication and related biases.. In: Rothstein HR, Sutton AJ, Borenstein M, eds. Publication Bias in Meta-Analysis—Prevention, Assessment and Adjustments. Chichester, UK: J Wiley; 2005:175-92. Google Scholar
Lau J, Ioannidis JP, Terrin N, Schmid CH, Olkin I. The case of the misleading funnel plot. BMJ. 2006;333:597-600. [PMID: 16974018] CrossrefMedlineGoogle Scholar
Ladabaum U, Chopra CL, Huang G, Scheiman JM, Chernew ME, Fendrick AM. Aspirin as an adjunct to screening for prevention of sporadic colorectal cancer. A cost-effectiveness analysis. Ann Intern Med. 2001;135:769-81. [PMID: 11694102] LinkGoogle Scholar
Deeks JJ. Systematic reviews in health care: Systematic reviews of evaluations of diagnostic and screening tests. BMJ. 2001;323:157-62. [PMID: 11463691] CrossrefMedlineGoogle Scholar
Altman DG. Systematic reviews of evaluations of prognostic variables. BMJ. 2001;323:224-8. [PMID: 11473921] CrossrefMedlineGoogle Scholar
Ioannidis JP, Ntzani EE, Trikalinos TA, Contopoulos-Ioannidis DG. Replication validity of genetic association studies. Nat Genet. 2001;29:306-9. [PMID: 11600885] CrossrefMedlineGoogle Scholar
Lavis J, Davies H, Oxman A, Denis JL, Golden-Biddle K, Ferlie E. Towards systematic reviews that inform health care management and policy-making. J Health Serv Res Policy. 2005;10 Suppl 135-48. [PMID: 16053582] CrossrefMedlineGoogle Scholar
Stewart LA, Clarke MJ. Practical methodology of meta-analyses (overviews) using updated individual patient data. Cochrane Working Group. Stat Med. 1995;14:2057-79. [PMID: 8552887] CrossrefMedlineGoogle Scholar
Moja LP, Telaro E, D'Amico R, Moschetti I, Coe L, Liberati A. Assessment of methodological quality of primary studies by systematic reviews: results of the metaquality cross sectional study. BMJ. 2005;330:1053. [PMID: 15817526] CrossrefMedlineGoogle Scholar
Guyatt GH, Oxman AD, Vist GE, Kunz R, Falck-Ytter Y, Alonso-Coello P, et al; GRADE Working Group. GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. BMJ. 2008;336:924-6. [PMID: 18436948] CrossrefMedlineGoogle Scholar
Schünemann HJ, Jaeschke R, Cook DJ, Bria WF, El-Solh AA, Ernst A, et al; ATS Documents Development and Implementation Committee. An official ATS statement: grading the quality of evidence and strength of recommendations in ATS guidelines and recommendations. Am J Respir Crit Care Med. 2006;174:605-14. [PMID: 16931644] CrossrefMedlineGoogle Scholar
Chan AW, Hróbjartsson A, Haahr MT, Gøtzsche PC, Altman DG. Empirical evidence for selective reporting of outcomes in randomized trials: comparison of protocols to published articles. JAMA. 2004;291:2457-65. [PMID: 15161896] CrossrefMedlineGoogle Scholar
Chan AW, Krleza-Jerić K, Schmid I, Altman DG. Outcome reporting bias in randomized trials funded by the Canadian Institutes of Health Research. CMAJ. 2004;171:735-40. [PMID: 15451835] CrossrefMedlineGoogle Scholar
Silagy CA, Middleton P, Hopewell S. Publishing protocols of systematic reviews: comparing what was done to what was planned. JAMA. 2002;287:2831-4. [PMID: 12038926] CrossrefMedlineGoogle Scholar
Author, Article, and Disclosure Information
From Ottawa Methods Centre, Ottawa Hospital Research Institute, University of Ottawa, Ottawa, Ontario, Canada; Università di Modena e Reggio Emilia, Modena, Italy; Centro Cochrane Italiano, Istituto Ricerche Farmacologiche Mario Negri, Milan, Italy; and Centre for Statistics in Medicine, University of Oxford, Oxford, United Kingdom.
Acknowledgment: The following people contributed to the PRISMA Statement: Doug Altman, DSc, Centre for Statistics in Medicine (Oxford, United Kingdom); Gerd Antes, PhD, University Hospital Freiburg (Freiburg, Germany); David Atkins, MD, MPH, Health Services Research & Development Service, Veterans Health Administration (Washington, DC); Virginia Barbour, MRCP, DPhil, PLoS Medicine (Cambridge, United Kingdom); Nick Barrowman, PhD, Children's Hospital of Eastern Ontario (Ottawa, Ontario, Canada); Jesse A. Berlin, ScD, Johnson & Johnson Pharmaceutical Research and Development (Titusville, New Jersey); Jocalyn Clark, PhD, PLoS Medicine (at the time of writing, BMJ; London, United Kingdom); Mike Clarke, PhD, UK Cochrane Centre (Oxford, United Kingdom) and School of Nursing and Midwifery, Trinity College (Dublin, Ireland); Deborah Cook, MD, Departments of Medicine, Clinical Epidemiology and Biostatistics, McMaster University (Hamilton, Ontario, Canada); Roberto D'Amico, PhD, Università di Modena e Reggio Emilia (Modena, Italy) and Centro Cochrane Italiano, Istituto Ricerche Farmacologiche Mario Negri (Milan, Italy); Jonathan J. Deeks, PhD, University of Birmingham (Birmingham, United Kingdom); P.J. Devereaux, MD, PhD, Departments of Medicine, Clinical Epidemiology and Biostatistics, McMaster University (Hamilton, Ontario, Canada); Kay Dickersin, PhD, Johns Hopkins Bloomberg School of Public Health (Baltimore, Maryland); Matthias Egger, MD, Department of Social and Preventive Medicine, University of Bern (Bern, Switzerland); Edzard Ernst, MD, PhD, FRCP, FRCP(Edin), Peninsula Medical School (Exeter, United Kingdom); Peter C. Gøtzsche, MD, MSc, The Nordic Cochrane Centre (Copenhagen, Denmark); Jeremy Grimshaw, MBChB, PhD, FRCFP, Ottawa Hospital Research Institute (Ottawa, Ontario, Canada); Gordon Guyatt, MD, Departments of Medicine, Clinical Epidemiology and Biostatistics, McMaster University (Hamilton, Ontario, Canada); Julian Higgins, PhD, MRC Biostatistics Unit (Cambridge, United Kingdom); John P.A. Ioannidis, MD, University of Ioannina Campus (Ioannina, Greece); Jos Kleijnen, MD, PhD, Kleijnen Systematic Reviews Ltd (York, United Kingdom) and School for Public Health and Primary Care (CAPHRI), University of Maastricht (Maastricht, the Netherlands); Tom Lang, MA, Tom Lang Communications and Training (Davis, California); Alessandro Liberati, MD, Università di Modena e Reggio Emilia (Modena, Italy) and Centro Cochrane Italiano, Istituto Ricerche Farmacologiche Mario Negri (Milan, Italy); Nicola Magrini, MD, NHS Centre for the Evaluation of the Effectiveness of Health Care–CeVEAS (Modena, Italy); David McNamee, PhD, The Lancet (London, United Kingdom); Lorenzo Moja, MD, MSc, Centro Cochrane Italiano, Istituto Ricerche Farmacologiche Mario Negri (Milan, Italy); David Moher, PhD, Ottawa Methods Centre, Ottawa Hospital Research Institute (Ottawa, Ontario, Canada); Cynthia Mulrow, MD, MSc, Annals of Internal Medicine (Philadelphia, Pennsylvania); Maryann Napoli, Center for Medical Consumers (New York, New York); Andy Oxman, MD, Norwegian Health Services Research Centre (Oslo, Norway); Ba' Pham, MMath, Toronto Health Economics and Technology Assessment Collaborative (Toronto, Ontario, Canada; at the time of the first meeting of the group, GlaxoSmithKline Canada [Mississauga, Ontario, Canada]); Drummond Rennie, MD, FRCP, FACP, University of California, San Francisco (San Francisco, California); Margaret Sampson, MLIS, Children's Hospital of Eastern Ontario (Ottawa, Ontario, Canada); Kenneth F. Schulz, PhD, MBA, Family Health International (Durham, North Carolina); Paul G. Shekelle, MD, PhD, Southern California Evidence-Based Practice Center (Santa Monica, California); Jennifer Tetzlaff, BSc, Ottawa Methods Centre, Ottawa Hospital Research Institute (Ottawa, Ontario, Canada); David Tovey, FRCGP, The Cochrane Library, Cochrane Collaboration (Oxford, United Kingdom; at the time of the first meeting of the group, BMJ [London, United Kingdom]); and Peter Tugwell, MD, MSc, FRCPC, Institute of Population Health, University of Ottawa (Ottawa, Ontario, Canada).
Grant Support: PRISMA was funded by the Canadian Institutes of Health Research; Università di Modena e Reggio Emilia, Italy; Cancer Research UK; Clinical Evidence BMJ Knowledge; The Cochrane Collaboration; and GlaxoSmithKline, Canada. Dr. Liberati is funded, in part, through grants of the Italian Ministry of University (COFIN-PRIN 2002 prot. 2002061749 and COFIN-PRIN 2006 prot. 2006062298). Dr. Altman is funded by Cancer Research UK. Dr. Moher is funded by a University of Ottawa Research Chair. None of the sponsors had any involvement in the planning, execution, or write-up of the PRISMA documents. Additionally, no funder played a role in drafting the manuscript.
Disclosures: None disclosed.
Corresponding Author: David Moher, PhD, Ottawa Methods Centre, Ottawa Hospital Research Institute, The Ottawa Hospital, General Campus, Critical Care Wing (Eye Institute), 6th Floor, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada; e-mail, dmoher@ohri.
Current Author Addresses: Dr. Moher and Ms. Tetzlaff: Ottawa Methods Centre, Ottawa Hospital Research Institute, The Ottawa Hospital, General Campus, Critical Care Wing (Eye Institute), 6th Floor, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada.
Dr. Liberati: Università di Modena e Reggio Emilia and Centro Cochrane Italiano, Istituto Ricerche Farmacologiche Mario Negri, Via La Masa 19, 20156 Milan, Italy.
Dr. Altman: Centre for Statistics in Medicine, University of Oxford, Wolfson College Annexe, Linton Road, Oxford OX2 6UD, United Kingdom.
* Membership of the PRISMA Group is provided in the Acknowledgment.