Case-control studies are perhaps the most frequent form of analytic study design.  These designs are very good for events that are rare in occurrence..

Still, there are some situations where cohort study designs would be appropriate in the field. The classic design in a cohort study is shown here.  The study begins by assessing baseline levels of the exposure and other variables.  Study subjects are then followed on a regular basis to identify the outcome.  The frequency of outcomes are tested between persons who had exposure to the possible risk factor at baseline and persons with no exposure.