Appendix to Chapter 4 Clinical epidemiology. What it can and cannot tell us

Abstract Statistical techniques have been developed and refined to help detect the causes of human disease. Since these techniques were first applied to infectious diseases, this medical discipline is called epidemiology, a term originally referring to its application to epidemic diseases such as smallpox, plague, and so on. Epidemiology attempts to relate the occurrence of disease in a given population to some common factor. Early examples include the relation of cholera to consumption of infected drinking water, and the association of some forms of lung cancer with cigarette smoking. Most epidemiological studies are either retrospective or prospective. In the former, patients with a particular disease are studied to identify aspects of their lifestyle that may be common to them all. By contrast, prospective studies examine a population and see what happens to the individuals with time. An example would be measuring the level of selenium in the blood of 5000 patients and then following them to see which developed cancer or heart disease.