The epidemiology of depressive disorder.

The concept of depression is reviewed. Depression is defined as a syndrome and thus involves particularly subjective decisions by the diagnostician. The conceptual difficulties which arise from this are outlined. The rate of risk is reviewed, using both studies of treated cases and community interview surveys. The study of treated rates tells more of the variables affecting the process of declaration than of depression. It is proposed that case-finding has the prerequisite of precise case-definition with a standardized instrument. Only then can comparability be reached. The effect sociodemographic variables on rates of risk is analysed: it is concluded that they do not account for much of the variance because they are at best gross measures. The role of life events is assessed and it is argued that only by the study of their possible interactions with other factors will an adequate causal explanation of depression be achieved. The usefulness of this as a validation of the concept of depression is emphasized. In this paper we shall firstly look at how concepts of depression affect the process of arriving at a diagnosis and secondly at policies of case finding. We are then in a position to survey critically the findings of epidemiology in the study of depression. Finally, we will review work which throws light on the social causation of depression with the emphasis on recent developments.