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': 'Cause to effect progression is seen in all EXCEPT- \nSelect and explain. \nA. Case control study, B. Ecological study, C. Coho study, D. Randomized control trail', 'role': 'user'}, {'content': 'Answer: A \nExplanation: a case control study is always employed in such diseases where an exposure and outcome had already occurred.it is a retrospective kind of study in which the study always progresses from effect to cause. ref:park&;s textbook of preventive and social medicine,22nd edition,pg no 71', 'role': 'assistant'}]