Pharmacovigilance is the science and activities relating to the detection, assessment, understanding, and prevention of adverse drug effects or any drug-related problem. It requires a large sum of data to validate the results whereas in the retrospective method the nature of the study group was defined precisely. Definite criteria were established so that there was no uncertainty about types of cases and stages of growth development which was included in or excluded from the study. The choice of case and control was guided by the concern of validity. The advantage of retrospective studies was...