[The decision to treat based on epidemiological methodology: the paradigm of hypercholesterolemia].

The author reviews the epidemiological methods, both non experimental and experimental, founding evidence-based medicine. As an example, he reviews the evolution of the scientific knowledge about the relationship between hypercholesterolemia and coronary heart disease and about the determinants of the serum cholesterol concentration. Epidemiology studies the causal chain between exposure and event (sickness) and proposes, within the framework of primary and secondary prevention of coronary heart disease, interventions to interrupt the causal chain at a given level.