The Strengthening the Reporting of
Observational Studies in Epidemiology (STROBE)
Statement: Guidelines for Reporting
Erik von Elm1*, Douglas G. Altman2, Matthias Egger1,3, Stuart J. Pocock4, Peter C. Gøtzsche5,
Jan P. Vandenbroucke6for the STROBE Initiative
1 Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland, 2 Centre for Statistics in Medicine, University of Oxford, Oxford, United Kingdom,
3 Department of Social Medicine, University of Bristol, Bristol, United Kingdom, 4 London School of Hygiene and Tropical Medicine, University of London, London, United
Kingdom, 5 Nordic Cochrane Centre, Copenhagen, Denmark, 6 Department of Clinical Epidemiology, Leiden University Hospital, Leiden, The Netherlands
Funding: The workshop was funded
by the European Science Foundation
(ESF). Additional funding was
received from the Medical Research
Council Health Services Research
Collaboration and the National
Health Services Research and
Programme. The funders had no role
in study design, data collection and
analysis, decision to publish, or
preparation of the manuscript.
Competing Interests: The authors
have declared that no competing
Citation: von Elm E, Altman DG,
Egger M, Pocock SJ, Gøtzsche PC, et
al. (2007) The Strengthening the
Reporting of Observational Studies in
Epidemiology (STROBE) Statement:
Guidelines for reporting
observational studies. PLoS Med
4(10): e296. 10.1371/journal.pmed.
Received: June 20, 2007
Accepted: August 30, 2007
Published: October 16, 2007
Copyright: ? 2007 von Elm et al. This
is an open-access article distributed
under the terms of the Creative
Commons Attribution License, which
permits unrestricted use, distribution,
and reproduction in any medium,
provided the original author and
source are credited. For details on
further use, see the STROBE Web site
In order to encourage dissemination
of the STROBE Statement, this article
will also be published and made freely
available by Annals of Internal
Medicine, BMJ, Bulletin of the World
Health Organization, Epidemiology,
The Lancet, and Preventive Medicine.
Consolidated Standards of Reporting
Trials; STREGA, STROBE Extension to
Genetic Association Studies; STROBE,
Strengthening the Reporting of
Observational Studies in
* To whom correspondence should
be addressed. E-mail: strobe@ispm.
A B S T R A C T
Much biomedical research is observational. The reporting of such research is often
inadequate, which hampers the assessment of its strengths and weaknesses and of a study’s
generalisability. The Strengthening the Reporting of Observational Studies in Epidemiology
(STROBE) Initiative developed recommendations on what should be included in an accurate
and complete report of an observational study. We defined the scope of the recommendations
to cover three main study designs: cohort, case-control, and cross-sectional studies. We
convened a 2-day workshop in September 2004, with methodologists, researchers, and journal
editors to draft a checklist of items. This list was subsequently revised during several meetings
of the coordinating group and in e-mail discussions with the larger group of STROBE
contributors, taking into account empirical evidence and methodological considerations. The
workshop and the subsequent iterative process of consultation and revision resulted in a
checklist of 22 items (the STROBE Statement) that relate to the title, abstract, introduction,
methods, results, and discussion sections of articles. 18 items are common to all three study
designs and four are specific for cohort, case-control, or cross-sectional studies. A detailed
Explanation and Elaboration document is published separately and is freely available on the
Web sites of PLoS Medicine, Annals of Internal Medicine, and Epidemiology. We hope that the
STROBE Statement will contribute to improving the quality of reporting of observational
PLoS Medicine | www.plosmedicine.orgOctober 2007 | Volume 4 | Issue 10 | e296 1623
P PL Lo oS S MEDICINE
Many questions in medical research are investigated in
observational studies . Much of the research into the cause
of diseases relies on cohort, case-control, or cross-sectional
studies. Observational studies also have a role in research into
the benefits and harms of medical interventions . Rando-
mised trials cannot answer all important questions about a
given intervention. For example, observational studies are
more suitable to detect rare or late adverse effects of
treatments, and are more likely to provide an indication of
what is achieved in daily medical practice .
Research should be reported transparently so that readers
can follow what was planned, what was done, what was found,
and what conclusions were drawn. The credibility of research
depends on a critical assessment by others of the strengths
and weaknesses in study design, conduct, and analysis.
Transparent reporting is also needed to judge whether and
how results can be included in systematic reviews [4,5].
However, in published observational research important
information is often missing or unclear. An analysis of
epidemiological studies published in general medical and
specialist journals found that the rationale behind the choice
of potential confounding variables was often not reported .
Only few reports of case-control studies in psychiatry
explained the methods used to identify cases and controls
. In a survey of longitudinal studies in stroke research, 17 of
49 articles (35%) did not specify the eligibility criteria .
Others have argued that without sufficient clarity of report-
ing, the benefits of research might be achieved more slowly
, and that there is a need for guidance in reporting
observational studies [10,11].
Recommendations on the reporting of research can
improve reporting quality. The Consolidated Standards of
Reporting Trials (CONSORT) Statement was developed in
1996 and revised 5 years later . Many medical journals
supported this initiative , which has helped to improve
the quality of reports of randomised trials [14,15]. Similar
initiatives have followed for other research areas—e.g., for
the reporting of meta-analyses of randomised trials  or
diagnostic studies . We established a network of method-
ologists, researchers, and journal editors to develop recom-
mendations for the reporting of observational research: the
Strengthening the Reporting of Observational Studies in
Epidemiology (STROBE) Statement.
Aims and Use of the STROBE Statement
The STROBE Statement is a checklist of items that should
be addressed in articles reporting on the 3 main study designs
of analytical epidemiology: cohort, case-control, and cross-
sectional studies. The intention is solely to provide guidance
on how to report observational research well: these recom-
mendations are not prescriptions for designing or conduct-
ing studies. Also, while clarity of reporting is a prerequisite to
evaluation, the checklist is not an instrument to evaluate the
quality of observational research.
Here we present the STROBE Statement and explain how it
was developed. In a detailed companion paper, the Explan-
ation and Elaboration article [18–20], we justify the inclusion
of the different checklist items and give methodological
background and published examples of what we consider
transparent reporting. We strongly recommend using the
STROBE checklist in conjunction with the explanatory
article, which is available freely on the Web sites of PLoS
Medicine (http://www.plosmedicine.org/), Annals of Internal
Medicine (http://www.annals.org/), and Epidemiology (http://
Development of the STROBE Statement
We established the STROBE Initiative in 2004, obtained
funding for a workshop and set up a Web site (http://www.
strobe-statement.org/). We searched textbooks, bibliographic
databases, reference lists, and personal files for relevant
material, including previous recommendations, empirical
studies of reporting and articles describing relevant meth-
odological research. Because observational research makes
use of many different study designs, we felt that the scope of
STROBE had to be clearly defined early on. We decided to
focus on the 3 study designs that are used most widely in
analytical observational research: cohort, case-control, and
We organised a 2-day workshop in Bristol, UK, in
September 2004. 23 individuals attended this meeting,
including editorial staff from Annals of Internal Medicine,
BMJ, Bulletin of the World Health Organization, International
Journal of Epidemiology, JAMA, Preventive Medicine, and The
Lancet, as well as epidemiologists, methodologists, statisti-
cians, and practitioners from Europe and North America.
Written contributions were sought from 10 other individuals
who declared an interest in contributing to STROBE, but
could not attend. Three working groups identified items
deemed to be important to include in checklists for each type
of study. A provisional list of items prepared in advance
(available from our Web site) was used to facilitate dis-
cussions. The 3 draft checklists were then discussed by all
participants and, where possible, items were revised to make
them applicable to all three study designs. In a final plenary
session, the group decided on the strategy for finalizing and
disseminating the STROBE Statement.
After the workshop we drafted a combined checklist
including all three designs and made it available on our
Web site. We invited participants and additional scientists
and editors to comment on this draft checklist. We
subsequently published 3 revisions on the Web site, and 2
summaries of comments received and changes made. During
this process the coordinating group (i.e., the authors of the
present paper) met on eight occasions for 1 or 2 days and
held several telephone conferences to revise the checklist and
to prepare the present paper and the Explanation and
Elaboration paper [18–20]. The coordinating group invited 3
additional co-authors with methodological and editorial
expertise to help write the Explanation and Elaboration
paper, and sought feedback from more than 30 people, who
are listed at the end of this paper. We allowed several weeks
for comments on subsequent drafts of the paper and
reminded collaborators about deadlines by e-mail.
The STROBE Statement is a checklist of 22 items that we
consider essential for good reporting of observational studies
(Table 1). These items relate to the article’s title and abstract
PLoS Medicine | www.plosmedicine.org October 2007 | Volume 4 | Issue 10 | e2961624
Table 1. The STROBE Statement—Checklist of Items That Should Be Addressed in Reports of Observational Studies
TITLE and ABSTRACT1 (a) Indicate the study’s design with a commonly used term in the title or the abstract
(b) Provide in the abstract an informative and balanced summary of what was done and what was found
2 Explain the scientific background and rationale for the investigation being reported
3State specific objectives, including any prespecified hypotheses
Present key elements of study design early in the paper
Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection
(a) Cohort study—Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of
Case-control study—Give the eligibility criteria, and the sources and methods of case ascertainment and control selection. Give
the rationale for the choice of cases and controls
Cross-sectional study—Give the eligibility criteria, and the sources and methods of selection of participants
(b) Cohort study—For matched studies, give matching criteria and number of exposed and unexposed
Case-control study—For matched studies, give matching criteria and the number of controls per case
Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicable
For each variable of interest, give sources of data and details of methods of assessment (measurement).
Describe comparability of assessment methods if there is more than one group
Describe any efforts to address potential sources of bias
Explain how the study size was arrived at
Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen, and why
12 (a) Describe all statistical methods, including those used to control for confounding
(b) Describe any methods used to examine subgroups and interactions
(c) Explain how missing data were addressed
(d) Cohort study—If applicable, explain how loss to follow-up was addressed
Case-control study—If applicable, explain how matching of cases and controls was addressed
Cross-sectional study—If applicable, describe analytical methods taking account of sampling strategy
(e) Describe any sensitivity analyses
Participants 13*(a) Report the numbers of individuals at each stage of the study—e.g., numbers potentially eligible, examined for eligibility, con-
firmed eligible, included in the study, completing follow-up, and analysed
(b) Give reasons for non-participation at each stage
(c) Consider use of a flow diagram
(a) Give characteristics of study participants (e.g., demographic, clinical, social) and information on exposures and potential con-
(b) Indicate the number of participants with missing data for each variable of interest
(c) Cohort study—Summarise follow-up time (e.g., average and total amount)
Cohort study—Report numbers of outcome events or summary measures over time
Case-control study—Report numbers in each exposure category, or summary measures of exposure
Cross-sectional study—Report numbers of outcome events or summary measures
(a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (e.g., 95% confidence interval).
Make clear which confounders were adjusted for and why they were included
(b) Report category boundaries when continuous variables were categorized
(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period
Report other analyses done—e.g., analyses of subgroups and interactions, and sensitivity analyses
Summarise key results with reference to study objectives
Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude
of any potential bias
Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar stu-
dies, and other relevant evidence
Discuss the generalisability (external validity) of the study results
Funding22Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the
present article is based
*Give such information separately for cases and controls in case-control studies, and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE checklist
is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at http://www.annals.org/, and
Epidemiology at http://www.epidem.com/). Separate versions of the checklist for cohort, case-control, and cross-sectional studies are available on the STROBE Web site at http://www.
PLoS Medicine | www.plosmedicine.org October 2007 | Volume 4 | Issue 10 | e2961625
(item 1), the introduction (items 2 and 3), methods (items 4–
12), results (items 13–17) and discussion sections (items 18–
21), and other information (item 22 on funding). 18 items are
common to all three designs, while four (items 6, 12, 14, and
15) are design-specific, with different versions for all or part
of the item. For some items (indicated by asterisks),
information should be given separately for cases and controls
in case-control studies, or exposed and unexposed groups in
cohort and cross-sectional studies. Although presented here
as a single checklist, separate checklists are available for each
of the 3 study designs on the STROBE Web site.
Implications and Limitations
The STROBE Statement was developed to assist authors
when writing up analytical observational studies, to support
editors and reviewers when considering such articles for
publication, and to help readers when critically appraising
published articles. We developed the checklist through an
open process, taking into account the experience gained with
previous initiatives, in particular CONSORT. We reviewed
the relevant empirical evidence as well as methodological
work, and subjected consecutive drafts to an extensive
iterative process of consultation. The checklist presented
here is thus based on input from a large number of
individuals with diverse backgrounds and perspectives. The
comprehensive explanatory article [18–20], which is intended
for use alongside the checklist, also benefited greatly from
this consultation process.
Observational studies serve a wide range of purposes, on a
continuum from the discovery of new findings to the
confirmation or refutation of previous findings [18–20]. Some
studies are essentially exploratory and raise interesting
hypotheses. Others pursue clearly defined hypotheses in
available data. In yet another type of studies, the collection of
new data is planned carefully on the basis of an existing
hypothesis. We believe the present checklist can be useful for
all these studies, since the readers always need to know what
was planned (and what was not), what was done, what was
found, and what the results mean. We acknowledge that
STROBE is currently limited to three main observational
study designs. We would welcome extensions that adapt the
checklist to other designs—e.g., case-crossover studies or
ecological studies—and also to specific topic areas. Four
extensions are now available for the CONSORT statement
[21–24]. A first extension to STROBE is underway for gene-
disease association studies: the STROBE Extension to Genetic
Association studies (STREGA) initiative . We ask those
who aim to develop extensions of the STROBE Statement to
contact the coordinating group first to avoid duplication of
The STROBE Statement should not be interpreted as an
attempt to prescribe the reporting of observational research
in a rigid format. The checklist items should be addressed in
sufficient detail and with clarity somewhere in an article, but
the order and format for presenting information depends on
author preferences, journal style, and the traditions of the
research field. For instance, we discuss the reporting of
results under a number of separate items, while recognizing
that authors might address several items within a single
section of text or in a table. Also, item 22, on the source of
funding and the role of funders, could be addressed in an
appendix or in the methods section of the article. We do not
aim at standardising reporting. Authors of randomised
clinical trials were asked by an editor of a specialist medical
journal to ‘‘CONSORT’’ their manuscripts on submission
. We believe that manuscripts should not be ‘‘STROBEd’’,
in the sense of regulating style or terminology. We encourage
authors to use narrative elements, including the description
of illustrative cases, to complement the essential information
about their study, and to make their articles an interesting
We emphasise that the STROBE Statement was not
developed as a tool for assessing the quality of published
observational research. Such instruments have been devel-
oped by other groups and were the subject of a recent
systematic review . In the Explanation and Elaboration
paper, we used several examples of good reporting from
studies whose results were not confirmed in further research
– the important feature was the good reporting, not whether
the research was of good quality. However, if STROBE is
adopted by authors and journals, issues such as confounding,
bias, and generalisability could become more transparent,
which might help temper the over-enthusiastic reporting of
new findings in the scientific community and popular media
, and improve the methodology of studies in the long
term. Better reporting may also help to have more informed
decisions about when new studies are needed, and what they
We did not undertake a comprehensive systematic review
for each of the checklist items and sub-items, or do our own
research to fill gaps in the evidence base. Further, although
no one was excluded from the process, the composition of the
group of contributors was influenced by existing networks
and was not representative in terms of geography (it was
dominated by contributors from Europe and North America)
and probably was not representative in terms of research
interests and disciplines. We stress that STROBE and other
recommendations on the reporting of research should be
seen as evolving documents that require continual assess-
ment, refinement, and, if necessary, change. We welcome
suggestions for the further dissemination of STROBE—e.g.,
by re-publication of the present article in specialist journals
and in journals published in other languages. Groups or
individuals who intend to translate the checklist to other
languages should consult the coordinating group beforehand.
We will revise the checklist in the future, taking into account
comments, criticism, new evidence, and experience from its
use. We invite readers to submit their comments via the
STROBE Web site (http://www.strobe-statement.org/).
We are grateful to Gerd Antes, Kay Dickersin, Shah Ebrahim, and
Richard Lilford for supporting the STROBE Initiative. We are
grateful to the following institutions that have hosted working
meetings of the coordinating group: Institute of Social and
Preventive Medicine (ISPM), University of Bern, Bern, Switzerland;
Department of Social Medicine, University of Bristol, Bristol, UK;
London School of Hygiene and Tropical Medicine, London, UK;
Nordic Cochrane Centre, Copenhagen, Denmark; and Centre for
Statistics in Medicine, Oxford, UK. We are grateful to six reviewers
who provided helpful comments on a previous draft of this paper.
Contributors to the STROBE Initiative
The following individuals have contributed to the content and
elaboration of the STROBE Statement: Douglas G Altman, Maria
Blettner, Paolo Boffetta, Hermann Brenner, Genevie `ve Che ˆne, Cyrus
PLoS Medicine | www.plosmedicine.orgOctober 2007 | Volume 4 | Issue 10 | e296 1626
Cooper, George Davey-Smith, Erik von Elm, Matthias Egger, France
Gagnon, Peter C Gøtzsche, Philip Greenland, Sander Greenland,
Claire Infante-Rivard, John Ioannidis, Astrid James, Giselle Jones,
Bruno Ledergerber, Julian Little, Margaret May, David Moher,
Hooman Momen, Alfredo Morabia, Hal Morgenstern, Cynthia D
Mulrow, Fred Paccaud, Stuart J Pocock, Charles Poole, Martin Ro ¨o ¨sli,
Dietrich Rothenbacher, Kenneth Rothman, Caroline Sabin, Willi
Sauerbrei, Lale Say, James J Schlesselman, Jonathan Sterne, Holly
Syddall, Jan P Vandenbroucke, Ian White, Susan Wieland, Hywel
Williams, Guang Yong Zou.
Author contributions. The authors coordinated the STROBE
Initiative and contributed to the writing of the paper. EvE wrote
the first draft of the paper and takes care of most of the practical
coordination of STROBE. ME initiated STROBE and, together with
EvE, organised the first workshop.
1. Glasziou P, Vandenbroucke JP, Chalmers I (2004) Assessing the quality of
research. BMJ 328: 39–41.
2.Black N (1996) Why we need observational studies to evaluate the
effectiveness of health care. BMJ 312: 1215–1218.
3.Papanikolaou PN, Christidi GD, Ioannidis JP (2006) Comparison of
evidence on harms of medical interventions in randomized and non-
randomized studies. CMAJ 174: 635–641.
4. Ju ¨ni P, Altman DG, Egger M (2001) Systematic reviews in health care:
Assessing the quality of controlled clinical trials. BMJ 323: 42–46.
5.Egger M, Schneider M, Davey Smith G (1998) Spurious precision? Meta-
analysis of observational studies. BMJ 316: 140–144.
6. Pocock SJ, Collier TJ, Dandreo KJ, de Stavola BL, Goldman MB, et al. (2004)
Issues in the reporting of epidemiological studies: a survey of recent
practice. BMJ 329: 883.
7. Lee W, Bindman J, Ford T, Glozier N, Moran P, et al. (2007) Bias in
psychiatric case-control studies: literature survey. Br J Psychiatry 190: 204–
8. Tooth L, Ware R, Bain C, Purdie DM, Dobson A (2005) Quality of reporting
of observational longitudinal research. Am J Epidemiol 161: 280–288.
9. Bogardus ST Jr., Concato J, Feinstein AR (1999) Clinical epidemiological
quality in molecular genetic research: the need for methodological
standards. JAMA 281: 1919–1926.
10. Anonymous (1981) Guidelines for documentation of epidemiologic studies.
Epidemiology Work Group of the Interagency Regulatory Liaison Group.
Am J Epidemiol 114: 609–613.
11. Rennie D (2001) CONSORT revised—improving the reporting of random-
ized trials. JAMA. 285: 2006–2007.
12. Moher D, Schulz KF, Altman DG (2001) The CONSORT statement: revised
recommendations for improving the quality of reports of parallel-group
randomised trials. Lancet 357: 1191–1194.
13. Moher D, Altman DG, Schulz KF, Elbourne DR (2004) Opportunities and
challenges for improving the quality of reporting clinical research:
CONSORT and beyond. CMAJ 171: 349–350.
14. Plint AC, Moher D, Morrison A, Schulz K, Altman DG, et al. (2006) Does the
CONSORT checklist improve the quality of reports of randomised
controlled trials? A systematic review. Med J Aust 185: 263–267.
15. Egger M, Ju ¨ni P, Bartlett C (2001) Value of flow diagrams in reports of
randomized controlled trials. JAMA 285: 1996–1999.
16. Moher D, Cook DJ, Eastwood S, Olkin I, Rennie D, et al. (1999) Improving
the quality of reports of meta-analyses of randomised controlled trials: the
QUOROM statement. Quality of Reporting of Meta-analyses. Lancet 354:
17. Bossuyt PM, Reitsma JB, Bruns DE, Gatsonis CA, Glasziou PP, et al. (2003)
Towards complete and accurate reporting of studies of diagnostic
accuracy: The STARD Initiative. Ann Intern Med. 138: 40–44.
18. Vandenbroucke JP, von Elm E, Altman DG, Gøtzsche PC, Mulrow CD, et al.
for the STROBE Initiative (2007) Strengthening the Reporting of
Observational Studies in Epidemiology (STROBE): Explanation and
Elaboration. PLoS Med 4: e297. doi:10.1371/journal.pmed.0040297
19. Vandenbroucke JP, von Elm E, Altman DG, Gøtzsche PC, Mulrow CD, et al.
for the STROBE Initiative (2007) Strengthening the Reporting of
Observational Studies in Epidemiology (STROBE): Explanation and
Elaboration. Ann Intern Med. In press.
20. Vandenbroucke JP, von Elm E, Altman DG, Gøtzsche PC, Mulrow CD, et al.
for the STROBE Initiative (2007)
Observational Studies in Epidemiology (STROBE): Explanation and
Elaboration. Epidemiology. In press.
21. Ioannidis JP, Evans SJ, Gøtzsche PC, O’Neill RT, Altman DG, et al. (2004)
Better reporting of harms in randomized trials: an extension of the
CONSORT statement. Ann Intern Med 141: 781–788.
22. Campbell MK, Elbourne DR, Altman DG (2004) CONSORT statement:
extension to cluster randomised trials. BMJ 328: 702–708.
23. Piaggio G, Elbourne DR, Altman DG, Pocock SJ, Evans SJ (2006) Reporting
of noninferiority and equivalence randomized trials: an extension of the
CONSORT statement. JAMA 295: 1152–1160.
24. Gagnier JJ, Boon H, Rochon P, Moher D, Barnes J, et al. (2006) Reporting
randomized, controlled trials of herbal interventions: an elaborated
CONSORT statement. Ann Intern Med 144: 364–367.
25. Ioannidis JP, Gwinn M, Little J, Higgins JP, Bernstein JL, et al. (2006) A road
map for efficient and reliable human genome epidemiology. Nat Genet 38:
26. Ormerod AD (2001) CONSORT your submissions: an update for authors.
Br J Dermatol 145: 378–379.
27. Schriger DL (2005) Suggestions for improving the reporting of clinical
research: the role of narrative. Ann Emerg Med 45: 437–443.
28. Sanderson S, Tatt ID, Higgins JP (2007) Tools for assessing quality and
susceptibility to bias in observational studies in epidemiology: a systematic
review and annotated bibliography. Int J Epidemiol 36: 666–676.
29. Bartlett C, Sterne J, Egger M (2002) What is newsworthy? Longitudinal
study of the reporting of medical research in two British newspapers. BMJ
Strengthening the Reporting of
PLoS Medicine | www.plosmedicine.org October 2007 | Volume 4 | Issue 10 | e2961627