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Preferred reporting items for systematic reviews
and meta‐analyses: the PRISMA Statement
David Moher, Alessandro Liberati , Jenni fer Tetzlaff, Douglas G Altman,
The PRISMA Group
David Moher is at the Ottawa Methods Centre, Ottawa Hospital Research Institute, and the Department of Epidemiology and
Community Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada. Alessandro Liberati is at the
Università di Modena e Reggio Emilia, Modena, and the Centro Cochrane Italiano, Istituto Ricerche Farmacologiche Mario
Negri, Milan, Italy. Jennifer Tetzlaff is at the Ottawa Methods Centre, Ottawa Hospital Research Institute, Ottawa, Ontario.
Douglas G Altman is at the Centre for Statistics in Medicine, University of Oxford, Oxford, United Kingdom. Membership of the
PRISMA Group is provided in the Acknowledgements.
Competing interests: None declared.
Funding source: 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.
Alessandro Liberati is funded, in part, through grants of the Italian Ministry of University (COFIN ‐ PRIN 2002 prot. 2002061749
and COFIN ‐ PRIN 2006 prot. 2006062298). Douglas G Altman is funded by Cancer Research UK. David 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.
Correspondence: Dr. David Moher, dmoher@ohri.ca
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,3and some
health care journals are moving in this direction.4As
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 4 leading medical journals in 1985 and
1986 and found that none met all 8 explicit scientific
criteria, such as a quality assessment of included
studies.5In 1987, Sacks and colleagues6evaluated the
adequacy of reporting of 83 meta-analyses on 23
characteristics in 6 domains. Reporting was generally
poor; between 1 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 OfMeta-analyses), which focused on the
reporting of meta-analyses of randomized controlled
trials.8In 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).
Terminology
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.9A systematic review is a
review of a clearly formulated question that uses
systematic and explicit methods to identify, select, and
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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 3-day meeting was held in Ottawa, 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 Website.
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 update11 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
question16,17 and providing greater
transparency when updating systematic
reviews.
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The PRISMA Statement
The PRISMA Statement consists of a 27-item checklist
(Table 1; see also for a downloadable template for
researchers to re-use) and a 4-phase flow diagram
(Figure 1; see also Figure S1 for a downloadable
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
Figure 1: Flow of information through the different phases of a systematic review
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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
.
Endorsement
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 Website. 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
produced18 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.
Discussion
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 existence28 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 diagnostic32 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 document18 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 endeavour, 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
website. We will use such information to inform
PRISMA's continued development.
Supporting Information
Downloadable versions of Figure S1 and Text S1 can be
found online at http://www.openmedicine.ca/article/
view/285/247.
Note: To encourage dissemination of the PRISMA Statement,
this article is freely accessible on the Open Medicine
website (http://openmedicine.ca/) and the PLoS Medicine
website (http://plosmedicine.org/) and is also published in
the Annals of Internal Medicine,BMJ, and Journal of
Clinical Epidemiology. The authors jointly hold the copyright
Review Moher et al
Open Medicine 2009 3(2) :1 23-1 30
of this article. For details on further use, see the PRISMA
website (http://prisma‐statement.org/). The PRISMA
Explanation and Elaboration Paper is available at the PLoS
Medicine website (http://www.plosmedicine.org/article/
info:doi/10.1371/journal.pmed.1000100).
Acknowledgments: The following people contributed to the
PRISMA Statement: Doug Altman, DSc, Centre for Statistics in
Medicine (Oxford, UK); Gerd Antes, PhD, University Hospital
Freiburg (Freiburg, Germany); David Atkins, MD, MPH, Health
Services Research and Development Service, Veterans Health
Administration (Washington, D. C., US); Virginia Barbour,
MRCP, DPhil, PLoS Medicine (Cambridge, UK); Nick
Barrowman, PhD, Children's Hospital of Eastern Ontario
(Ottawa, Canada); Jesse A. Berlin, ScD, Johnson & Johnson
Pharmaceutical Research and Development (Titusville, New
Jersey, US); Jocalyn Clark, PhD, PLoS Medicine (at the time
of writing, BMJ, London, UK); Mike Clarke, PhD, UK Cochrane
Centre (Oxford, UK) and School of Nursing and Midwifery,
Trinity College (Dublin, Ireland); Deborah Cook, MD,
Departments of Medicine, Clinical Epidemiology and
Biostatistics, McMaster University (Hamilton, 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, UK);
P. J. Devereaux, MD, PhD, Departments of Medicine, Clinical
Epidemiology and Biostatistics, McMaster University
(Hamilton, Canada); Kay Dickersin, PhD, Johns Hopkins
Bloomberg School of Public Health (Baltimore, Maryland,
US); 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, UK); Peter C. Gøtzsche, MD, MSc, The Nordic
Cochrane Centre (Copenhagen, Denmark); Jeremy Grimshaw,
MBChB, PhD, FRCFP, Ottawa Hospital Research Institute
(Ottawa, Canada); Gordon Guyatt, MD, Departments of
Medicine, Clinical Epidemiology and Biostatistics, McMaster
University (Hamilton, Canada); Julian Higgins, PhD, MRC
Biostatistics Unit (Cambridge, UK); John P. A. Ioannidis, MD,
University of Ioannina Campus (Ioannina, Greece); Jos
Kleijnen, MD, PhD, Kleijnen Systematic Reviews Ltd (York,
UK) and School for Public Health and Primary Care (CAPHRI),
University of Maastricht (Maastricht, Netherlands); Tom
Lang, MA, Tom Lang Communications and Training (Davis,
California, US); 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,
UK); 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, Canada); Cynthia Mulrow, MD,
MSc, Annals of Internal Medicine (Philadelphia, Pennsylvania,
US); Maryann Napoli, Center for Medical Consumers (New
York, New York, US); Andy Oxman, MD, Norwegian Health
Services Research Centre (Oslo, Norway); Ba' Pham, MMath,
Toronto Health Economics and Technology Assessment
Collaborative (Toronto, Canada) (at the time of the first
meeting of the group, GlaxoSmithKline Canada, Mississauga,
Canada); Drummond Rennie, MD, FRCP, FACP, University of
California San Francisco (San Francisco, California, US);
Margaret Sampson, MLIS, Children's Hospital of Eastern
Ontario (Ottawa, Canada); Kenneth F. Schulz, PhD, MBA,
Family Health International (Durham, North Carolina, US);
Paul G. Shekelle, MD, PhD, Southern California Evidence
Based Practice Center (Santa Monica, California, US);
Jennifer Tetzlaff, BSc, Ottawa Methods Centre, Ottawa
Hospital Research Institute (Ottawa, Canada); David Tovey,
FRCGP, The Cochrane Library, Cochrane Collaboration
(Oxford, UK) (at the time of the first meeting of the group,
BMJ, London, UK); Peter Tugwell, MD, MSc, FRCPC, Institute
of Population Health, University of Ottawa (Ottawa,
Canada).
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Contributors: David Moher, Alessandro Liberati, and Douglas
Altman wrote the first draft of the paper. They also
participated in regular conference calls, identified the
participants, secured funds, planned the meeting,
participated in the meeting, and drafted the manuscript.
Jennifer Tetzlaff participated in identifying the evidence
base for PRISMA, refining the checklist, and drafting the
manuscript. All of the authors contributed to the writing of
the paper and agreed with the recommendations.
Citation: Moher D, Liberati A, Tetzlaff J, Altman DG; The
PRISMA Group. Preferred reporting items for systematic
reviews and meta‐analyses: the PRISMA Statement Open Med
2009;3(2):123‐130
Published: 21 July 2009
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