<prompt> Which one of the following statements regarding prepost clinical trial is most appropriate ?They cannot be randomizedThey are useful in studies involving moalityThey use the patient as his or her own controlThey are usually easier to interpret than the comparable parallel clinical trial  <response>: 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. 