<prompt> In a case-control study of a suspected association between breast cancer and the contraceptive pill, all of the following are true statements except?The control should come from a population that has the same potential for breast cancer as the casesThe control should exclude women known to be taking the pill at the time of the surveryAll the controls need to be healthyThe attributable risk of breast cancer resulting from the pill may be directly measured  <response>: Ans. is d i.e., The attributable risk of breast cancer resulting from the pill may be directly measured AR calculation requires incidence which can be obtained from only a coho study Not from a case control study o In a Case Control Study, Cases are diseased and Controls are healthy o Controls should be similar to Cases in all respects for ensuring comparability o Cases should be matched with controls for all factors EXCEPT for the risk factor under study otherwise the etiological role of risk factor under study, would be eliminated from the study, since both groups are exactly similar in all respects; So if controls do not exclude women known to be taking the pill at the time of the survey, both groups will become similar in respect to risk factor contraceptive pill under study and no relationship can be established with breast cancer. 