Epidemiology

The branch of medicine concerned with the occurrence and distribution of disease, including infectious diseases and noninfectious diseases such as cancer. In epidemiological studies, the members of a population are counted and described in terms of such variables as race, sex, age, social class, occupation, and marital status. Then the incidence and prevalence of the disease of interest are determined. These observations may be repeated at regular intervals in order to detect changes over time. The result is a statistical record that may reveal links between particular variables and distribution of disease. In comparative epidemiological studies, two or more groups are chosen. For example, in a study of the link between smoking and lung cancer, one group may consist of smokers and the other of nonsmokers; the proportion with cancer in each group is calculated.