Clinical (Therapeutic) Trials
We start by recalling some facts from previous chapters. There, many examples of exposures have appeared such as genetic disposition, smoking, lack of education, poor hygiene, polluted water, crowded housing, malnutrition, use of contaminated needles by drug addicts, and unprotected sex; many more will be treated in later chapters. They all exist independently of the health system. They belong to the first four categories of risk factors listed in Sect. 1.5, that is genetic factors, environmental factors, life style, and social and economic conditions. The study of such risk factors is called “observational” or “analytic” epidemiology because one observes and analyzes already existing situations; see Sect. 15.3. Normally we are of course interested in the influence of factors that make the risk of disease, death etc. increase when their level increases.