The Incidence Cohort Study assesses the incidence of disease and seeks to identify risk factors for disease onset. It answers the question, “Is the incidence greater in those exposed than in those who are non-exposed?”

The Prognostic Cohort Study follows a diseased cohort to assess factors associated with the outcome. The outcome may be either recovery or death. The primary purpose is to identify all the explanatory factors for the outcome. Such explanatory factors are also known as prognostic factors.