independent studies to calculate an effect. X LEVEL 2 Cohort Studies: Studies observe large groups of people that record exposure to risk factors to find possible causes of disease. Studies gather data either moving forward (prospective) or review past data already recorded (retrospective). X LEVEL 3 Case Report Studies: Studies used to determine if there is an association between exposure and specific health outcome. Frequently used when studying rare health outcomes or diseases. X LEVEL 4 Case Report: Provides detailed report of diagnosis