Table 6.

STROBE statement—checklist of items that should be included in reports of observational studies

VariableItem No.RecommendationPage No.Relevant Text from Manuscript
Title and abstract1(1) Indicate the study’s design with a commonly used term in the title or the abstract3Retrospective
(2) Provide in the abstract an informative and balanced summary of what was done and what was found3Methods and Results sections of abstract
 Background/rationale2Explain the scientific background and rationale for the investigation being reported4All page 4
 Objectives3State specific objectives, including any prespecified hypotheses5Under: Objectives
 Study design4Present key elements of study design early in the paper4Last sentence
 Setting5Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection
 Participants6(1) 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 participantsPage 5: “Subjects and Measurements”
(2) 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 caseN/A
 Variables7Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicablePage 5: “Subjects and Measurements”
 Data sources/measurement8aFor 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 groupPage 5: “Subjects and Measurements”
 Bias9Describe any efforts to address potential sources of biasStatistical adjustments described on page 5.
 Study size10Explain how the study size was arrived atFull national experience: explicit
 Quantitative variables11Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and whyPage 5: “Subjects and Measurements”
 Statistical methods12(1) Describe all statistical methods, including those used to control for confoundingStatistical adjustments described on page 5.
(2) Describe any methods used to examine subgroups and interactionsAll subgroups of Table 1 were examined
(3) Explain how missing data were addressedVery low frequency; no imputation.
(4) 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 analytic methods taking account of sampling strategyN/A
(5) Describe any sensitivity analysesNone
 Participants13a(1) Report numbers of individuals at each stage of study—e.g., numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analyzedN/A
(2) Give reasons for nonparticipation at each stageN/A
(3) Consider use of a flow diagramN/A
 Descriptive data14a(1) Give characteristics of study participants (e.g., demographic, clinical, social) and information on exposures and potential confoundersTable 1
(2) Indicate number of participants with missing data for each variable of interestTable 1
(3) Cohort study—Summarize follow-up time (e.g., average and total amount)N/A
 Outcome data15aCohort study—Report numbers of outcome events or summary measures over timeN/A
Case-control studyReport numbers in each exposure category, or summary measures of exposureN/A
Cross-sectional studyReport numbers of outcome events or summary measuresTables 13
 Main results16(1) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (e.g., 95% CI). Make clear which confounders were adjusted for and why they were included95% CI, stated explicitly throughout.
(2) Report category boundaries when continuous variables were categorizedDone
(3) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time periodN/A
 Other analyses17Report other analyses done—e.g., analyses of subgroups and interactions, and sensitivity analysesDone
 Key results18Summarize key results with reference to study objectives8First line of Discussion
 Limitations19Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias11Second-to-last paragraph of Discussion.
 Interpretation20Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidenceLast paragraph of Discussion.
 Generalizability21Discuss the generalizability (external validity) of the study resultsThis is a full national sample
Other information
 Funding22Give the source of funding and the role of the funders for this study and, if applicable, for the original study on which this article is basedNot funded
  • An Explanation and Elaboration article discusses each checklist item and gives methodologic 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, Annals of Internal Medicine at, and Epidemiology at Information on the STROBE Initiative is available at STROBE, STrengthening the Reporting of OBservational studies in Epidemiology; N/A: not available.

  • a 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.