Alessandro Liberati, MD, DrPH; Douglas G. Altman, DSc; Jennifer Tetzlaff, BSc; Cynthia Mulrow, MD, MSc; Peter C. Gøtzsche, MD, DrMedSci, MSc; John P.A. Ioannidis, MD; Mike Clarke, BA, DPhil; P. J. Devereaux, MD, BSc, PhD; Jos Kleijnen, MD, PhD; David Moher, PhD
Acknowledgments: The following people contributed to this paper: 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 (Ottawa, Ontario, Canada). Dr. Lorenzo Moja helped with the preparation and the several updates of the manuscript and assisted with the preparation of the reference list. Dr. Liberati is the guarantor of the manuscript.
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.
Potential Financial Conflicts of Interest:Employment: M. Clarke (His employment is as Director of the UK Cochrane Centre. He is employed by the Oxford Radcliffe Hospitals Trust on behalf of the Department of Health and the National Institute for Health Research in England. This is a fixed-term contract, the renewal of which is dependent upon the value placed upon his work, that of the UK Cochrane Centre and of The Cochrane Collaboration more widely by the Department of Health. His work involves the conduct of systematic reviews and the support of the conduct and use of systematic reviews. Therefore, work—such as this manuscript—relating to systematic reviews might have an impact on his employment).
Corresponding Author: Alessandro Liberati, MD Università di Modena e Reggio Emilia, Centro Cochrane Italiano, Istituto Ricerche Farmacologiche Mario Negri, Via La Masa 19, 20156 Milan, Italy; e-mail, firstname.lastname@example.org.
Current Author Addresses: Dr. Liberati: Università di Modena e Reggio Emilia, 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.
Ms. Tetzlaff and Dr. Moher: 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. Mulrow: Annals of Internal Medicine, 190 N. Independence Mall West, Philadelphia, PA 19106.
Dr. Gøtzsche: Nordic Cochrane Centre, Rigshospitàlet, Dept 3343, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
Dr. Ioannidis: Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, University Campus, Ioannina 45110, Greece.
Dr. Clarke: School of Nursing and Midwifery, Trinity College, 24 D'Olier Street, Dublin 2, Ireland.
Dr. Devereaux: Clinical Epidemiology and Biostatistics, McMaster University Health Sciences Centre, Room 2C8 1200 Main Street West, Hamilton, Ontario L8N 3Z5, Canada.
Dr. Kleijnen: Kleijnen Systematic Reviews Ltd, Westminister Business Centre, 10 Great North Way, Nether Poppleton, York YO26 6RB, United Kingdom.
Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, 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-W-94. doi: 10.7326/0003-4819-151-4-200908180-00136
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Published: Ann Intern Med. 2009;151(4):W-65-W-94.
Systematic reviews and meta-analyses are essential to summarize evidence relating to efficacy and safety of health care interventions accurately and reliably. The clarity and transparency of these reports, however, is not optimal. Poor reporting of systematic reviews diminishes their value to clinicians, policy makers, and other users.
Since the development of the QUOROM (QUality Of Reporting Of Meta-analysis) Statement—a reporting guideline published in 1999—there have been several conceptual, methodological, and practical advances regarding the conduct and reporting of systematic reviews and meta-analyses. Also, reviews of published systematic reviews have found that key information about these studies is often poorly reported. Realizing these issues, an international group that included experienced authors and methodologists developed PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) as an evolution of the original QUOROM guideline for systematic reviews and meta-analyses of evaluations of health care interventions.
The PRISMA Statement consists of a 27-item checklist and a four-phase flow diagram. The checklist includes items deemed essential for transparent reporting of a systematic review. In this Explanation and Elaboration document, we explain the meaning and rationale for each checklist item. For each item, we include an example of good reporting and, where possible, references to relevant empirical studies and methodological literature. The PRISMA Statement, this document, and the associated Web site (www.prisma-statement.org) should be helpful resources to improve reporting of systematic reviews and meta-analyses.
Table 1. Checklist of Items to Include When Reporting a Systematic Review (With or Without Meta-Analysis)
Flow of information through the different phases of a systematic review.
Helping To Develop the Research Question(s): The PICOS Approach.
Identification of Study Reports and Data Extraction.
Study Quality and Risk of Bias.
Whether or Not To Combine Data.
Meta-Analysis and Assessment of Consistency (Heterogeneity).
Bias Caused by Selective Publication of Studies or Results Within Studies.
Example Figure: Example flow diagram of study selection.
DDW = Digestive Disease Week; UEGW = United European Gastroenterology Week. Reproduced with permission from reference 130.
Table 2. Example Table: Summary of Included Studies Evaluating the Efficacy of Antiemetic Agents in Acute Gastroenteritis
Table 3. Example Table: Quality Measures of the Randomized Controlled Trials That Failed to Fulfill Any One of Six Markers of Validity
Table 4. Example Table: Heterotopic Ossification in Trials Comparing Radiotherapy to Non-Steroidal Anti-Inflam- matory Drugs After Major Hip Procedures and Fractures
Example Figure: Overall failure (defined as failure of assigned regimen or relapse) with tetracycline-rifampicin versus tetracycline-streptomycin.
CI = confidence interval. Adapted with permission from reference 137.
Example Figure: Example of a funnel plot showing evidence of considerable asymmetry.
SE = standard error. Adapted with permission from reference 146.
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