<prompt> Cross product ratio is calculated in which studyCoho studyCase control studyCross sectional studyEcological study  <response>: 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 Odds ratio given by the formula ad bc. Ref:- K Park, 24th ed; pg num:- 78 