Case-control study
An observational study that compares the history of exposure to a particular risk factor or intervention for two groups of people from the same population, where one group has a specified outcome or disease (cases) and the other group does not (controls).
Note 1: Investigators retrospectively compare the histories (in terms of past exposure history to particular risk factors) of the cases and controls to determine whether there is an association between the outcome and the cause being studied.
Note 2: The groups should be similar in terms of certain characteristics, such as age and gender.
Note 3: The term "case-control study" is often incorrectly considered a synonym of retrospective study.