Research Design: Cohort Studies

In a cohort study, a group of subjects (the cohort) is followed for a period of time; assessments are conducted at baseline, during follow-up, and at the end of follow-up. Cohort studies are, therefore, empirical, longitudinal studies based on data obtained from a sample; they are also observational and (usually) naturalistic. Analyses can be conducted for the cohort as a whole or for subgroups amongst which comparisons can be drawn. Because there is no randomization to the subgroups of interest, cause and effect relationships cannot be determined, and relationships between variables must be stated as associations that may or may not be influenced by confounding. The cohort that is studied can be prospectively or retrospectively defined, and each method has its advantages and disadvantages. These and other issues are explained with the help of examples. A special note is made of cohort studies in Indian psychiatry.