This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: JIPMER 2017, Subject name: Social & Preventive Medicine
[{'content': 'Case acts as its own control in which of the following study? \nSelect and explain. \nA. Cross over study, B. Retrospective study, C. Prospective study, D. Case control study', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Advantages of cross-over study design ( Cross over RCT): Each patient serves as his own control. All patients can be assured that they will receive the new therapy sometime during the course of investigation ( Thus, no ethical issues). Economize the total number of patients.', 'role': 'assistant'}]