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': 'Causal association factors can be revealed by \nSelect and explain. \nA. Case control study, B. Coho study, C. Cross sectional study, D. Experimental study', 'role': 'user'}, {'content': "Answer: A \nExplanation: Case-control studies often retrospective studies are a common first approach to test the causal hypothesis. In recent years case-control study has emerged as a permanent method of epidemiological investigation. - Both exposure and outcome have occurred before the study. - The study proceeds backward from effect to cause. - It uses a control or comparison group to suppo or refute an inference Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 79", 'role': 'assistant'}]