This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Which one of the following statements regarding prepost clinical trial is most appropriate ? 
Select and explain. 
A. They cannot be randomized, B. They are useful in studies involving moality, C. They use the patient as his or her own control, D. They are usually easier to interpret than the comparable parallel clinical trial
C: They use the patient as his or her own control
Answer: C: They use the patient as his or her own control 
Explanation: Ans. is 'c' i.e., They use the patient as his or her own control Pre-post clinical trial o Pre-post clinical trials 'or' before and after comparison studies are Non randomized trials in which we compare the incidence of disease before and after introduction of a preventive measure. o The event which took place prior to the use of the new treatment or preventive procedure are used as a standard for comparison. In other words the experiment serves as its own control : this eliminates viually all group differences. o It is often used in assessing whether knowledge, attitudes or preexisting risk behavioral change when a subject is assigned to an intervention.