Cross product ratio is calculated in which study

Cross product ratio:- From a case control study, we can derive what is known as Odds Ratio (OR) which is a measure of the strength of the association between risk factor and outcome. Odds ratio is closely related to relative risk. The derivation of odds ratio is based on three assumptions : (a) the disease being investigated must be relatively rare; (b) the cases must be representative of those with the disease, and (c) the controls must be representative of those without the disease. Cross product ratio is the other name for Odd's ratio given by the formula ad/ bc. Ref:- K Park, 24th ed; pg num:- 78