Case–control studies

Case–control studies compare ill or injured individuals (cases) with those at risk of the illness or injury (controls) with regard to prior exposures or characteristics, and so appear to proceed backwards, from consequence to potential cause. They have the potential to identify associations that are not causal, either because of chance, or because of the influence of some other factor associated with both the exposure and outcome. However, if a case–control study is able to enrol cases and controls from the same underlying population at risk of the outcome, and can measure exposure status of these persons in a valid manner, the results obtained will closely resemble those of a properly performed cohort study.