STROBE INITIATIVE The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement Guidelines for Reporting Observational Studies

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 generalizability. 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 crosssectional 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 crosssectional 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 studies. (Epidemiology 2007;18: 800–804) 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 crosssectional studies. Observational studies also have a role in research into the benefits and harms of medical interventions. Randomized 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. 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 reporting, the benefits of research might be achieved more slowly, and that there is a need for guidance in reporting observational studies. 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 The workshop was funded by the European Science Foundation (ESF). Additional funding was received from the Medical Research Council Research and Development Programme and the Medical Research Council Health Services Research Collaboration and the National Health Services Research & Development Methodology Programme. Editors’ note: In order to encourage dissemination of the STROBE Statement, this article is freely accessible on the Web site of EPIDEMIOLOGY (www.epidem.com) and will also be published in Annals of Internal Medicine, BMJ, Bulletin of the World Health Organization, The Lancet, PLoS Medicine, and Preventive Medicine. The authors jointly hold the copyright of this article. For details on further use, see the STROBE website (www.strobe-statement.org). Related articles appear on pages 789, 791, 792, 794, 797, and 805. From the *Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland; †Centre for Statistics in Medicine, University of Oxford, Oxford UK; ‡Department of Social Medicine, University of Bristol, Bristol, UK; §London School of Hygiene and Tropical Medicine, University of London, London, UK; ¶Nordic Cochrane Centre, Copenhagen, Denmark; and Department of Clinical Epidemiology, Leiden University Hospital, Leiden, Netherlands. Correspondence: Erik von Elm, Institute of Social and Preventive Medicine (ISPM), University of Bern, Finkenhubelweg 11, CH-3012 Bern, Switzerland. E-mail: [email protected]. Copyright © 2007 by the authors ISSN: 1044-3983/07/1806-0800 DOI: 10.1097/EDE.0b013e3181577654 Epidemiology • Volume 18, Number 6, November 2007 800 quality of reports of randomized trials. Similar initiatives have followed for other research areas—eg, for the reporting of meta-analyses of randomized trials or diagnostic studies. We established a network of methodologists, researchers, and journal editors to develop recommendations 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 recommendations are not prescriptions for designing or conducting 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 Explanation and Elaboration article, –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 websites of PLoS Medicine (www.plosmedicine.org), Annals of Internal Medicine (www.annals.org), and EPIDEMIOLOGY (www.epidem.com). Development of the STROBE Statement We established the STROBE Initiative in 2004, obtained funding for a workshop and set up a website (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 methodological 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 cross-sectional studies. We organized 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, statisticians, 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 website) was used to facilitate discussions. 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 website. We invited participants and additional scientists and editors to comment on this draft checklist. We subsequently published 3 revisions on the website, and 2 summaries of comments received and changes made. During this process the coordinating group (ie, 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. The coordinating group invited 3 additional coauthors 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. STROBE Components 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 (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 website. 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 Epidemiology • Volume 18, Number 6, November 2007 STROBE Initiative for Reporting Observational Studies © 2007 the authors 801 TABLE 1. The STROBE statement—Checklist of Items That Should be Addressed in Reports of Observational Studies Item Number Recommendation TITLE and ABSTRACT 1 (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 INTRODUCTION Background/ rationale 2 Explain the scientific background and rationale for the investigation being reported Objectives 3 State specific objectives, including any prespecified hypotheses METHODS Study design 4 Present key elements of study design early in the paper Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection Participants 6 (a) Cohort study—Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up 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 Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicable Data sources/ measurement 8* 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 Bias 9 Describe any efforts to address potential sources of bias Study size 10 Explain how the study size was arrived at Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen, and why Statistical methods 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 RESULTS Participants 13* (a) Report the numbers of individuals at each stage of the study—eg, numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analyzed (b) Give reasons for non-participation at each stage (c) Consider use of a flow diagram Descriptive data 14* (a) Give characteristics of study participants (eg, demographic, clinical, social) and information on exposures and potential confounders (b) Indicate the number of participants with missing data for each variable of interest (c) Cohort study—Summarize follow-up time (eg, average and total amount) Outcome data 15* 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 Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, 95% confidence intervals). Make clear which confounders were adjusted for and why they were included (b) Report category boundaries when continuous variables were categorised (c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period Other analyses 17 Report other analyses done—eg, analyses of subgroups and interactions, and sensitivity analyses DISCUSSION Key results 18 Summarise key results with reference to study objectives Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence Generalizability 21 Discuss the generalizability (external validity) of the study results OTHER INFORMATION Funding 22 Give 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. 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 websites of PLoS Medicine, Annals of Internal Medicine, and EPIDEMIOLOGY). Separate versions of the checklist for cohort, case-control, and cross-sectional studies are available on the STROBE website. von Elm et al Epidemiology • Volume 18, Number 6, November 2007 © 2007 the authors 802 explanatory article, which is intended for use alongside the checklist, also benefited greatly from this consultation