EPIDEMIOLOGIC studies of mental disease may be divided into two major types: demographic, that is, concerned with descriptive epidemiology, and etiologic, or concerned with analytic epidemiology. In the first group are those studies which seek to determine the occurrence of mental diseases in the population in relation to demographic factors such as age, sex, race, marital status, social class, and area of residence. In the second are the studies which attempt to discover specific etiologic agents for mental diseases, such as bacteria and viruses, toxic agents, metabolic disorders, maternal complications and prematurity, hereditary factors, family interactions, and social stresses.
Demographic studies of disease are a useful tool in public health administration. They measure the size of the problem and thereby make possible a rational approach to the provision of hospital and clinic facilities. By defining those segments of the population with the greatest