The epidemiological study of depression in late life

Abstract

The epidemiological study on late life depression provides us with information on the distribution of the disorder in the aged population and the possible factors that influence its occurrence. Three basic resources have been used to study the epidemiology of psychiatric illness: psychiatric case registers, surveys of institutional and clinical populations, and general population surveys. Each of these has its value and limitations, as Blazer and Williams (1980) pointed out in their excellent review on the epidemiology of depression in late life. The results of field surveys are expressed in terms of incidence or prevalence of a disorder within a defined population. As far as incidence is concerned, it is necessary to survey a population on two separate occasions, the second survey serving to determine the number of persons who were not identified as ill on the first occasion but have subsequently become ill. The prevalence of a disorder can be estimated in a single survey. Because of these difficulties, comparatively few studies on the incidence of psychiatric disorders have been performed. In this paper, the author concentrates on prevalence studies of late life depression and discusses some sociocultural implications by comparing Western and Japanese studies. It is well known that estimated prevalence is different from true prevalence. The former is influenced by the way in which depressive symptoms develop clinically as a result of unfavourable life-