Cohort Study vs Case Study

Cohort Study, you are studying the risk factor and see if you can associate a disease to it. Therefore, you use Relative Risk and Attributable Risk. You can measure incidence in prospective and retrospective cohort studies. Note that cohort study can be retrospective i.e you follow the cohort in past time by checking their hospital records. For example, you can say the incidence of pulmonary tuberculosis was xx% in Asian immigrants who immigrated to the US in the period (2010-2013).

Case-Control Study, you are studying the disease and see if you can associate risk factors to it. Therefore, you use Odds Ratio. Case-Control Studies are typically done for rare diseases; you compare the small number of rare disease with a control group and find out if there was a risk factor that might have caused their disease. Commonly case control studies are retrospective.

For Example: If you make a study to find out the percentage of smokers among lung cancer patients versus the percentage of smokers among those who do not have lung cancer then this is case-control. Conversely, if you follow smokers and non-smokers in time and see who develop lung cancer or not, then this is a cohort study. Please see attached more info. Hope this helps.