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': 'A case control study is not characterized by- \nSelect and explain. \nA. Cases with the disease are compared to controls without the disease, B. Assessment of past exposure may be blased, C. Definition of cases may be difficult, D. Incidence rates may be computed directly', 'role': 'user'}, {'content': 'Answer: D \nExplanation: .<p>in case of a case control study ,we cannot measure incidence,and can only estimate the relative risk.and it doesnot distinguish between causes and associated factors.and it is also not suited to the evaluation of therapy or prophylaxis of disease.selectin of an appropriate control group may be difficult.</p><p>ref;parks textbook,22 nd ed,pg no 71</p>', 'role': 'assistant'}]