Which one of the following statements regarding prepost clinical trial is most appropriate ?

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.