case-control study

Syllable breakdown

Dictionary meaning

an observational study design that works backward from outcome to exposure: cases — people who have developed the disease or outcome of interest — are compared with controls — people from the same population who have not developed the outcome — to determine whether past exposure to a putative risk factor differs between the two groups; case-control studies are particularly efficient for studying rare diseases, which would require very large cohorts to observe adequate numbers of cases in a prospective design; the primary measure of association in a case-control study is the odds ratio — the ratio of the odds of exposure in cases to the odds of exposure in controls — which approximates the relative risk when the disease is rare; key methodological challenges include appropriate selection of controls, avoiding selection bias, and minimising recall bias — the tendency for cases to remember exposures more clearly than controls; Bradford Hill's work linking smoking to lung cancer used case-control methods pioneered by Doll and Hill

Examples

• The case-control study matched each meningitis case with four healthy controls from the same school, finding that sharing drinking vessels was a major risk factor.
• Nested case-control designs draw cases and controls from within an established cohort, combining the advantages of both study designs.