Case–Control Study

A case–control study is an observational study designed to determine if a risk factor is associated with an outcome of interest (disease or condition). This study design permits the researcher to determine if an exposure is associated with an outcome. First, a group with the outcome of interest (“cases”) is identified. Next, a group similar to cases (“controls”) is selected from the “study base” that yielded the cases but without the outcome of interest. Matching of cases and controls on certain characteristics ensures similarity and increases study efficiency. Historical risk factors in both groups are evaluated to determine whether some RFs occur more frequently in cases than controls. Case–control studies may establish an association between a risk factor and outcome but cannot demonstrate causation because of its retrospective nature. Compared to other study designs, case–control studies are inexpensive, quick, and allow the evaluation of several risk factors. Case–control study designs are useful for studying rare diseases, diseases with long latent periods, and for outbreak investigations. Limitations include selection bias and recall bias. Among the strategies to overcome selection bias include an appropriate sampling method, matching, using a minimum of two control groups, and drawing both cases and controls from the same population. Meanwhile, recall bias could be minimized by blinding.