Design-specific criteria to assess for risk of bias*
| Risk of bias | Criterion | Cohort | Case– control | Case series | Cross-sectional |
|---|---|---|---|---|---|
| Selection bias | Were participants analysed within the groups they were originally assigned to? | x | |||
| Did the study apply inclusion/exclusion criteria uniformly to all comparison groups? | x | x | |||
| Were cases and controls selected appropriately (eg, appropriate diagnostic criteria or definitions, equal application of exclusion criteria to case and controls, sampling not influenced by exposure status)? | x | ||||
| Did the strategy for recruiting participants into the study differ across study groups? | x | ||||
| Does the design or analysis control account for important confounding and modifying variables through matching, stratification, multivariable analysis or other approaches? | x | x | x | x | |
| Performance bias | Did researchers rule out any impact from a concurrent intervention or an unintended exposure that might bias results? | x | x | x | x |
| Did the study maintain fidelity to the intervention protocol? | x | x | x | ||
| Attrition bias | If attrition (overall or differential non-response, dropout, loss to follow-up or exclusion of participants) was a concern, were missing data handled appropriately (eg, intention-to-treat analysis and imputation)? | x | x | x | x |
| Detection bias | In prospective studies, was the length of follow-up different between the groups, or in case-control studies, was the time period between the intervention/exposure and outcome the same for cases and controls? | x | x | ||
| Were the outcome assessors blinded to the intervention or exposure status of participants? | x | x | x | x | |
| Were interventions/exposures assessed/defined using valid and reliable measures, implemented consistently across all study participants? | x | x | x | x | |
| Were outcomes assessed/defined using valid and reliable measures implemented consistently across all study participants? | x | x | x | x | |
| Were confounding variables assessed using valid and reliable measures implemented consistently across all study participants? | x | x | x | x | |
| Reporting bias | Were the potential outcomes prespecified by the researchers? Are all prespecified outcomes reported? | x | x | x | x |
*Adapted from Viswanathan et al.18