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
Case acts as its own control in which of the following study? 
Select and explain. 
A. Cross over study, B. Retrospective study, C. Prospective study, D. Case control study
A: Cross over study
Answer: A: Cross over study 
Explanation: 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.