Case-control studies are a nonexperimental form of medical research that informs cause-effect relationships. Their main purpose is the identification of risk factors for events of interest. Most famously, case-control studies provided the first evidence of a strong association between cigarette smoking and lung cancer. However, findings from a number of recent case-control studies have been subsequently contradicted or found to overestimate the strength of relationships compared with more robust epidemiological study designs. An example [Page 109]is the case-control finding that hormone replacement therapy (HRT) had a protective effect against coronary heart disease, following which randomized trial evidence identified a small increased risk associated with HRT.

Case-control studies identify cases as patients who already have a disease or condition of interest, and then attempt to identify characteristics ...