Least bias | Randomised, controlled trial or prospective cohort with a broad range (spectrum) of patients and controls, with masked (blinded) evaluation of the risk factor and disease outcome |
↓ | Prospective study of narrow spectrum patients, or retrospective study of broad spectrum (range) patients and controls. Risk factor measured in masked (blinded) fashion |
↓ | Retrospective study with narrow spectrum (range) patients and controls. Risk factor (case definition of coeliac) determined by someone other than the person who determined ataxia |
Most bias | Any study design where risk factor (eg, coeliac disease) criteria and outcome disease measurement are not applied independently, uncontrolled case series |