Figure 5. Diagram of a cohort study assessing whether lipid lowering is an independent predictor for the degree of benefit derived from statin therapy.

Experiments (top) generally assess interventions but can rarely directly assess their mechanisms of action. Cohort analyses (bottom) can provide evidence for or against proposed mechanisms of action by examining whether a marker for the proposed mechanism of action (i.e., low-density lipoprotein [LDL] cholesterol level) is an independent predictor of lower risk after controlling for treatment exposure, adherence, and other known risk factors for the outcome being studied. CV= cardiovascular.