case-control studies

Definition of case-control study
National Cancer Institute

case-control study

(kays-kun-TROLE STUH-dee)
A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called retrospective study.

Source: NCI Dictionary of Cancer Terms