Table 4: STROBE criteria scoring definitions.

Part of studyItemScore 1 if it

Title and abstract

1aIndicate study design with a commonly used term in the title or in the abstract(i) Mentions an explicit commonly used term for the study design in title or abstract
1b Provide in the abstract an informative and balanced summary of what was done and what was found(i) Includes a short description of the research question, methods, results, and conclusion
(ii) Provides only information presented in the article

Introduction

Background/rationale2Explain the scientific background and rationale for the investigation being reported(i) Provides important context, sets the stage for the study, and describes its focus
(ii) Provides an overview on what is known on a topic and what gaps in current knowledge are addressed by the study

Objectives3State specific objectives, including any prespecified hypotheses(i) States all original objectives
(ii) Specifies populations, exposures, outcomes, and parameters that will be estimated

Methods

Study design4Present key elements of study design early in the paper (i) Presents study design including source population of both cases and controls point in time the sample was taken, and if applicable the follow-up period

Setting5Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, followup, and data collection(i) Includes recruitment sites or sources
(ii) Refers to countries, towns, hospitals, or practices where the investigation took place

Participants6aCohort study—give the eligibility criteria and the sources and methods of selection of participants. Describe methods of followup
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
(i) Describes all eligibility criteria and also the group from which the population was selected
(ii) Details the description of methods of selection of all participants
(iii) Details the of follow-up procedures if applicable
6bCohort 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
(i) Describes matching criteria, numbers of exposed and unexposed or numbers of controls per case

Variables7Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicable(i) Defines all variables for and included in the analyses
(ii) Clearly describes definitions of diagnostic criteria for disease outcomes, disease events, or prevalent disease
(iii) Declares all candidate variables considered for statistical analysis

Data sources/measurement8For 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(i) Refers to studies that report validity or reliability of the outcome measure OR
(ii) Reports estimated validity or reliability

Bias9Describe any efforts to address potential sources of bias(i) Describes what measures were taken during the conduct of the study to reduce the potential of bias
(ii) If possible, discusses and estimates the direction and magnitude of bias

Study size10Explain how the study size was arrived at(i) Reports formal sample size calculations if they were done, or
(ii) Indicates the considerations that determined the study size

Quantitative variables11Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen, and why(i) For categorized variables, explains why and how data were grouped including the number of categories, the cut points, and category means or medians
(ii) For data presented in tabular forms, reports counts of cases, controls, persons at risk, and so forth for each category
(iii) For continuous variables, considers the nature of relation between exposure and outcome (linear, quadratic, normality, etc.).

Statistical methods12aDescribe all statistical methods, including those used to control for confounding(i) Describes statistical methods to enable a reader with access to the data to verify the reported results
12b Describe any methods used to examine subgroups and interactions(i) Describes what methods were used for subgroup analysis
(ii) Reports the way interaction effects were analyzed
12cExplain how missing data were addressed(i) If applicable, reports the number of missing values for each variable of interest and for each step in the analysis
(ii) Gives reason for missing values and indicates how many individuals were excluded because of missing data when describing the flow of participants through the study
(iii) Describes the nature of the analyses made for missing data
12dCohort study—if applicable, explain how loss to followup 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
(i) Cohort: reports on the number of individuals that were lost to follow-up and how those data were treated in the analyses
(ii) Case control: reports on how the matching was handled in the statistical analysis
(iii) Cross-sectional: reports on methods to adjust for complex sampling strategies if they were used (e.g., clustered sampling).
12eDescribe any sensitivity analyses(i) Describes sensitivity analyses, for example, used to identify the degree of confounding, selection bias, or information bias required to distort an association

Results

Participants13aReport the numbers of individuals at each stage of the study, for example, numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analyzed(i) Reports the number of individuals considered at each stage of the study from the stage of recruiting from the target population to the inclusion of participants’ data in the analysis: numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing followup, and analyzed
13bGive reasons for nonparticipation at each stage(i) If applicable, explains why participants no longer participated in the study or why they were excluded from further analysis
13cConsider use of a flow diagram(i) Especially for complex studies, not applicable for small cross-sectional studies

Descriptive data14aGive characteristics of study participants (e.g., demographic, clinical, and social) and information on exposures and potential confounders(i) Presents data as follows:
 continuous variables: mean + sd or median and percentile range
 categorical variables: number/proportion per category
14bIndicate the number of participants with missing data for each variable of interest(i) Explicitly mentions the number of participants with missing data, OR
(ii) Presents the data with sufficient details for the reader to see that all data were complete (especially for small studies)
14cCohort study—summarize follow-up time (e.g., average and total amount)

Outcome data15Cohort 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
(i) Presents descriptive data for exposure and outcome measures separately and not only the association between the measures

16aGive 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(i) Gives unadjusted estimates of effect size
(ii) If applicable, gives adjusted estimates of effect size
Main results16bReport category boundaries when continuous variables were categorized(i) Reports category boundaries when continuous variables were categorized
16cIf relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period(i) Only for ratio measures

Other analysis17Report other analyses done—for example, analyses of subgroups and interactions, and sensitivity analyses(i) Describes whether these analyses were planned in advance and which arose while analyzing

Discussion

Key results18Summarize key results with reference to study objectives(i) Begins the discussion with a short summary of the main findings of the study

Limitations19Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias(i) Mentions
 sources of bias and confounding
 direction of potential biases
 discusses any imprecision of results

Interpretation20Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence(i) Interprets the results taking into consideration the limitations of the study or bias.
(ii) Interprets the results in context of the existing external evidence from different types of studies.
(iii) Puts the results in context with similar studies and how the new study affects the existing body of evidence

Generalizability21Discuss the generalizability (external validity) of the study results(i) Gives sufficient information for the reader to judge the generalizability

Other information

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(i) Gives the source of funding
(ii) Describes the role of funders in detail