CHAPTER 17

STROBE (STrengthening theReporting of Observational
studies in Epidemiology)
Myriam Cevallos1 and Matthias Egger2
1 CTU Bern and Insititute of Social and Preventative Medicine, University of Bern, Bern, Switzerland
2 Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland

Timetable
Meeting/event date

Objective

March 2001
November 2001

Idea ﬁrst discussed
Small exploratory meeting at University of Bristol,
United Kingdom
Planning meeting at University of Bristol, United
Kingdom
Need for reporting guidelines discussed at World
Epidemiology Conference in Montreal, Canada
Large workshop at University of Bristol, funded by
European Science Foundation
First draft checklist posted on STROBE website
Publication of checklist and Explanation andElaboration document in several journals
Revision meeting at University of Bern, Switzerland

April 2003
August 2003
September 2004
May 2005
October 2007
August 2010

STROBE Statement
The STrengthening the Reporting of OBservational Studies in Epidemiology (STROBE) statement is a set of recommendations to improve thereporting of observational studies. STROBE addresses the three main typesof observational studies: cohort, case–control, and cross-sectional studies.
The statement consists of a checklist of 22 items that relate to the title,
abstract, introduction, methods, results, and discussion sections of articles.
Guidelines for Reporting Health Research: A User’s Manual, First Edition. Edited by David Moher,
Douglas G. Altman, Kenneth F. Schulz, Iveta Simera and Elizabeth Wager.
© 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.

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A diagram showing the number of individuals at each stage of the study, fromassessment of eligibility to inclusion in the analysis, may also be considered.
The STROBE checklist, the accompanying comprehensive Explanationand Elaboration (E&E) document, and the website, offer guidance toauthors on how to prepare reports on observational research, enhance
the completeness and transparency of reporting, and facilitate the criticalappraisal and interpretation of studies by reviewers, journal editors, andreaders.

History/development
The STROBE statement is the result of an international collaborative effort
by epidemiologists, methodologists, statisticians, and journal editors. The
idea of a reporting guideline for observational studies was ﬁrst discussed bya small group of epidemiologists working in the United Kingdom in 2001
and further developed in several meetings. The STROBE initiative wasformally established in 2004 in Bristol, United Kingdom, during a two-day
workshop funded by the European Science Foundation. In the same year,
the STROBE website (www.strobe-statement.org) was launched. Prior
to the workshop, the group conducted an extensive literature search of
textbooks, bibliographic databases, previous recommendations, etc., tocollect all relevant information related to observational research. The
group decided early on to restrict the scope of the STROBE statement tothree study designs.
The workshop was attended by 23 epidemiologists, methodologists,
statisticians, journal editors, and practitioners from Europe and North
America and was used to write the ﬁrst draft of the checklist. The draft
was subsequently revised during several meetings of the coordinationgroup and in email discussions with the wider group. Subsequently threerevisions were published on the website, two summaries of received
comments were prepared, and any changes were documented. During
this process, the coordinating group met on eight occasions and held
several telephone conferences to revise the checklist and to prepare thearticle reporting the STROBE statement as well as the E&E document.
The STROBE statement and the E&E paper were ﬁnally simultaneously
published in several journals, with open access to both articles.

When to use this guideline(what types of studies it covers)
The STROBE recommendations are designed to inform the reporting ofobservational epidemiological studies. STROBE covers descriptive studiesof, for example, the prevalence or incidence of a disease, as well as

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analytical studies that investigate associations between exposures andhealth outcomes. STROBE is limited to the three main observational study
designs: cohort, case–control, and cross-sectional studies.
The cohort design refers to studies where the investigators follow people
over time. They obtain information about people and their exposuresat baseline, let time pass, and then assess the occurrence of outcomes.
Investigators often compare people who are exposed to a factor of interest(e.g., particle matter in the air) with people who are not exposed or
exposed to a lesser degree, and assess exposure and outcome variables atmultiple points during follow-up. Incidence rates, rate ratios, and relative
risks may then be calculated.
In case–control studies, investigators compare exposures between people
with a particular disease outcome (cases) with people without that outcome (controls). All cases or a large fraction of cases diagnosed during aperiod are typically included in the study. The sample of controls represents
the cohort or population of people from which the cases arose. Dependingon the sampling strategy for cases and controls and the nature of the population studied, the odds ratio obtained in a case–control study is interpreted
as the risk ratio, rate ratio, or (prevalence) odds ratio [1].
In cross-sectional studies, investigators assess all individuals in a sample
at the same point in time, often to examine the prevalence of exposures,risk factors, or disease.
Other designs such as genetic linkage studies, infectious disease modeling or case reports and case series are not covered by STROBE. However, as
many of the key elements in STROBE also apply to these designs, authors
who report such studies may nevertheless ﬁnd the recommendations useful. The STROBE statement was not developed to assess the methodologicalquality of epidemiological studies and should not be used for this purpose.

Current versions
The STROBE statement includes a checklist of 22 items that relate to
the title, abstract, introduction, methods, results, and discussion sectionsof articles. Eighteen items are common to cohort studies, case–control
studies, and cross-sectional studies and four items are speciﬁc to each of
the three study designs. For some items, information should be given
separately for cases and controls in case–control studies or exposed andunexposed groups in cohort and cross-sectional studies. Separate checklists
for each of the three study designs are available on the STROBE website.
The E&E paper offers detailed explanations of each checklist item, gives
methodological background, and provides published examples of what the
STROBE group considered transparent reporting.

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The STROBE recommendations have so far been published in eight journals, including the BMJ, Annals of Internal Medicine, PLoS Medicine, and The
Lancet [2–9]. The E&E article was published in PLoS Medicine, Annals of Internal Medicine, and Epidemiology [10–12].

Previous versions
No major changes to the original version have been published.

Extensions to be aware of
The STrengthening the REporting of Genetic Association (STREGA)
recommendations were published in 2009 and are the ﬁrst extension of
STROBE [13]. STREGA provides additions to 12 of the 22 original itemsof the STROBE checklist to facilitate the reporting of genetic association
studies. An extension in the ﬁeld of molecular epidemiology has been
published [27] and one on neuro-epidemiology is in preparation.

Translations
The STROBE recommendations have been translated into Chinese,
Spanish, German, Italian, Japanese, Portuguese, Greek, and Persian.
Translations to French, Korean, and Bahasa Indonesian are under way.
The E&E document is available in Spanish, Japanese, and a Korean version
will become available soon.

Related activities
An idea that was discussed during the 2010 workshop was to bring STROBE
and PRISMA together and extend the PRISMA guidelines [14] for systematic reviews and meta-analyses of clinical trials to observational studies. In
the ﬁrst step, conceptual issues speciﬁc to observational studies were identiﬁed and the ﬁrst impression was gained of the PRISMA items that would
need to be changed and the new items that may need to be added.

How best to use the guideline
We strongly recommend authors to use the checklist alongside the STROBE
E&E document when writing reports of observational studies, to make sure

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that they understand what is meant (and what is not) by a given item.
Many authors will also ﬁnd the examples of good reporting useful. The
STROBE website may also be useful to identify additional information andbackground. The STROBE checklist can also support editors and reviewers
when assessing submitted articles for completeness of reporting of important methodological details.
The recommendations are only intended to provide guidance on how toreport observational research in a transparent and complete manner. They
are not prescriptions for designing or conducting studies or an instrument
to assess the quality of published articles.

Development process
The STROBE statement and other reporting guidelines should be considered as evolving documents that require periodic changes and updates inlight of experience and new evidence [15]. Indeed, two distinguished commentators argued that STROBE should come with an “expiration date,” andshould be updated in 2010 [16]. This was the aim of the workshop held inBern, Switzerland, in August 2010.
During this workshop the group discussed the impact of STROBE and
its endorsement by journals, and the uses (and misuses) of STROBE.
The group revisited the checklist to identify items in need of revisionand discussed the addition of new items, based on recent developments
in study methodology and new empirical evidence on the reporting ofcohort, case–control, and cross-sectional studies. The group identiﬁed
only minor revisions and additions, and it was felt that these did notjustify a new version of the checklist. A draft of a revised checklist withthe suggestions for modiﬁcations proposed during the meeting will serveas the basis for further discussions at the next meeting.

Evidence of effectiveness of guideline
The possible contribution of the STROBE statement in improving thequality of reporting of observational studies has been a matter for discussion and criticism in more than 30 commentaries and editorials [17]. The
fact that the STROBE website receives about 3000 hits per month gives
further indication of its impact.
Several recent bibliographic studies have used the STROBE statement toassess the quality of reporting of observational studies in deﬁned medicalﬁelds [18–24]. We are, however, not aware of any systematic study

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Guidelines for Reporting Health Research: A User’s Manualcomparing the quality of reporting before and after the publication of the
STROBE guidelines.

Endorsement and adherence
The STROBE recommendations have been cited over 600 times and havebeen endorsed by over 100 journals and the International Committee ofMedical Journal Editors (see website for complete list of endorsing journals)[17]. The type of endorsement and instructions to authors on the use of
STROBE, however, vary widely between journals.

Cautions and limitations (including scope)
The STROBE developers stress that their recommendations are about
reporting and should not be seen as prescriptions for designing or conducting studies. Moreover, the checklist should not be used as an instrument
to evaluate the quality of observational research. In a recent bibliographic
study [25] we looked at a sample of 100 randomly selected articles andexamined where, when, and why STROBE was cited. We found that inmost observational study reports, STROBE was used as a reporting guideline, whereas half of systematic reviews used STROBE inappropriately as atool to assess the methodological quality of studies. The absence of reliable
tools to assess the quality of observational studies [26] may explain why
authors sometimes use reporting guidelines for this purpose.
The STROBE recommendations are limited to three common observational study designs but do not cover many other designs and variations
that exist in epidemiological research. The group welcomes extensions that
adapt the checklist to other study designs.

Creators’ preferred bits
The creators of STROBE do not have preferred items as such, but generally
feel that the items closely linked to the prevention of bias in a given observational study are those where transparent and complete reporting is most
likely to make a difference. These items will vary between the different
study designs and within designs from study to study.

Future plans
The STROBE group will meet again in one or two years to review the needfor a revision of the statement. The group is in the process of developing a

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short checklist for journal and conference abstracts of observational studies based on the STROBE statement. Last but not least and also resulting
from our ﬁrst revision meeting in 2010, we plan to explore an extension of
the PRISMA recommendations for systematic reviews and meta-analysesof observational studies.

References
1 Knol, M.J. (2008) What do case-control studies estimate? Survey of methods andassumptions in published case-control research. American Journal of Epidemiology, 168(9), 1073–1081.
2 von Elm, E., Altman, D.G., Egger, M. et al. (2007) The Strengthening the Reporting ofObservational Studies in Epidemiology (STROBE) statement: guidelines for reporting
observational studies. Lancet, 370 (9596), 1453–1457.
3 von Elm, E. et al. (2007) The Strengthening the Reporting of Observational Studies
in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
Epidemiology, 18 (6), 800–804.
4 von Elm, E. et al. (2007) The Strengthening the Reporting of Observational Studies
in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
Bulletin of the World Health Organization, 85 (11), 867–872.
5 von Elm, E. et al. (2007) The Strengthening the Reporting of Observational Studies
in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
Preventive Medicine, 45 (4), 247–251.
6 von Elm, E. et al. (2007) Strengthening the Reporting of Observational Studies in
Epidemiology (STROBE) statement: guidelines for reporting observational studies.
BMJ, 335 (7624), 806–808.
7 von Elm, E. et al. (2007) The Strengthening the Reporting of Observational Studies
in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
PLoS Medicine, 4 (10), e296.
8 von Elm, E. et al. (2007) The Strengthening the Reporting of Observational Studies
in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
Annals of Internal Medicine, 147 (8), 573–577.
9 von Elm, E. et al. (2008) The Strengthening the Reporting of Observational Studies
in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
Journal of Clinical Epidemiology, 61 (4), 344–349.
10 Vandenbroucke, J.P. et al. (2007) Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. Epidemiology, 18 (6),805–835.
11 Vandenbroucke, J.P. et al. (2007) Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. PLoS Medicine, 4 (10),e297.
12 Vandenbroucke, J.P. et al. (2007) Strengthening the Reporting of Observational
Studies in Epidemiology (STROBE): explanation and elaboration. Annals of Internal
Medicine, 147 (8), W163–W194.
13 Little, J. et al. (2009) STrengthening the REporting of Genetic Association Studies(STREGA): an extension of the STROBE statement. PLoS Medicine, 6 (2), e22.
14 Liberati, A. et al. (2009) The PRISMA statement for reporting systematic reviews andmeta-analyses of studies that evaluate health care interventions: explanation andelaboration. PLoS Medicine, 6 (7), e1000100.

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15 Moher, D. et al. (2010) Guidance for developers of health research reporting guidelines. PLoS Medicine, 7 (2), e1000217.
16 Rothman, K.J. & Poole, C. (2007) Some guidelines on guidelines: they should comewith expiration dates. Epidemiology, 18 (6), 794–796.
17 STROBE statement. Strengthening the reporting of observational studies in epidemiology. Available from http://www.strobe-statement.org/.
18 Langan, S. et al. (2010) The reporting of observational research studies in dermatology
journals: a literature-based study. Archives of Dermatology, 146 (5), 534–541.
19 Brand, R.A. (2009) Standards of reporting: the CONSORT, QUORUM, and STROBE
guidelines. Clinical Orthopaedics and Related Research, 467 (6), 1393–1394.
20 Fung, A.E. et al. (2009) Applying the CONSORT and STROBE statements to evaluate the reporting quality of neovascular age-related macular degeneration studies.
Ophthalmology, 116 (2), 286–296.
21 Lystad, R.P., Pollard, H. & Graham, P.L. (2009) Epidemiology of injuries in competition taekwondo: a meta-analysis of observational studies. Journal of Science andMedicine in Sport, 12 (6), 614–621.
22 Papathanasiou, A.A. & Zintzaras, E. (2010) Assessing the quality of reporting of observational studies in cancer. Annals of Epidemiology, 20 (1), 67–73.
23 Theobald, K. et al. (2009) Quality assurance in non-interventional studies. German
Medical Science, 7, Doc29.
24 Yoon, U. & Knobloch, K. (2010) Quality of reporting in sports injury prevention
abstracts according to the CONSORT and STROBE criteria: an analysis of the World
Congress of Sports Injury Prevention in 2005 and 2008. British Journal of Sports
Medicine, 46 (3), 202–206.
25 Da Costa, B., Cevallos, M., Altman, D.G. et al. (2011) Uses and misuses of the STROBE
statement: bibliographic study. BMJ Open; 1:e000048.
26 Sanderson, S., Tatt, I.D. & Higgins, J.P. (2007) Tools for assessing quality and susceptibility to bias in observational studies in epidemiology: a systematic review andannotated bibliography. International Journal of Epidemiology, 36 (3), 666–676.
27 Gallo, V., Egger, M., McCormack, V. et al. (2011) STrengthening the Reporting ofOBservational studies in Epidemiology – Molecular Epidemiology (STROBE-ME): an
extension of the STROBE Statement. PLoS Med.; 8:e1001117.

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STROBE statement – checklist of items that should be included in reports of observational
studies
Item
No

Recommendation

1(a) Indicate the study’s design with a commonly used term in thetitle or the abstract(b) Provide in the abstract an informative and balanced summaryof what was done and what was foundBackground/rationale

2

Objectives

3

Explain the scientiﬁc background and rationale for theinvestigation being reported
State speciﬁc objectives, including any prespeciﬁed hypotheses

Title and abstract

Introduction

Methods
Study design
Setting

45Participants

6

Variables

7

Data sources/
measurement

8∗

Bias
Study size

9
10

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 datacollection(a) Cohort study – Give the eligibility criteria, and the sources
and methods of selection of participants. Describe methodsof follow-up
Case-control study – Give the eligibility criteria, and thesources and methods of case ascertainment and control
selection. Give the rationale for the choice of cases andcontrols
Cross-sectional study – Give the eligibility criteria, and thesources 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(continued)

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Item
No

Recommendation

Quantitative variables

11

Statistical methods

12

Explain how quantitative variables were handled in the analyses.
If applicable, describe which groupings were chosen and why(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 ofcases and controls was addressed
Cross-sectional study – If applicable, describe analyticalmethods taking account of sampling strategy(e) Describe any sensitivity analyses

Results
Participants

13∗

Descriptive data

14∗

Outcome data

15∗

Main results

16(a) Report numbers of individuals at each stage of study – eg
numbers potentially eligible, examined for eligibility, conﬁrmed 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 (eg demographic,clinical, social) and information on exposures and potential
confounders(b) Indicate number of participants with missing data for eachvariable of interest(c) Cohort study – Summarise follow-up time (eg, average andtotal amount)
Cohort study – Report numbers of outcome events or summary
measures over timeCase-control study – Report numbers in each exposure
category, or summary measures of exposure
Cross-sectional study – Report numbers of outcome events orsummary measures(a) Give unadjusted estimates and, if applicable, confounderadjusted estimates and their precision (eg, 95% conﬁdence
interval). Make clear which confounders were adjusted for
and why they were included(b) Report category boundaries when continuous variables werecategorized(c) If relevant, consider translating estimates of relative risk into
absolute risk for a meaningful time period

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Item
No

Recommendation

17

Report other analyses done – eg analyses of subgroups andinteractions, and sensitivity analyses

Key results
Limitations

18
19

Interpretation

20

Generalisability

21

Summarise key results with reference to study objectives
Discuss limitations of the study, taking into account sources ofpotential bias or imprecision. Discuss both direction andmagnitude of any potential bias
Give a cautious overall interpretation of results considering
objectives, limitations, multiplicity of analyses, results fromsimilar studies, and other relevant evidence
Discuss the generalisability (external validity) of the study results

Other analyses
Discussion

Other information
Funding

22

Give the source of funding and the role of the funders for thepresent study and, if applicable, for the original study on
which the present article is based∗ Give 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/). Information on the
STROBE Initiative is available at www.strobe-statement.org.