This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'In case control study of buccal carcinoma- \nSelect and explain. \nA. CA is commoner in zarda pan users than non users, B. Zarda pan is a cause of buccal CA, C. Zarda pan is associated with buccal CA, D. If use of zarda pan is stopped, number of cases will reduce', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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)', 'role': 'assistant'}]