genetic association investigation case control genetic association study The case group and control group are differed by their phenotyp outcome measurement, for example, the case group is a group of people that has disease A, but control group has no disease A. Usually other characteristics of the control and case group are carefully matched (e.g. by age, sex, enviroment) to avoid other variables's co-effets on the variable that is under investigation. Genetic association investigation that use to observe the non-random differences of a genetic factor's frequency between case group and control group.