<prompt> In case control study of buccal carcinoma-CA is commoner in zarda pan users than non usersZarda pan is a cause of buccal CAZarda pan is associated with buccal CAIf use of zarda pan is stopped, number of cases will reduce  <response>: Case control studies often retrospective studies are a common first approach to test causal hypothesis. In recent years case control study has emerged as a permanent method of epidemiological investigation. Both exposure and outcome has occurred before the study. Study proceeds backwards from effect to cause. It uses a control or comparison group to suppo or refute an inference refer pgno:71 park 23 rd edition 