Methodological issues in psychiatric case-identification

The use of the term 'case' in clinical psychiatric research implies that the investigator wishes to identify the presence or absence of some clinically relevant disorder or disorders in a human population; for example, to distinguish X from non-X, Y from non-Y, and X from Y. The main reasons for making such identifications are to clarify or refine the descriptive features of the disorder, to calculate an incidence or a prevalence rate, and to test hypotheses concerning, for example, causes, treatments or outcomes. Many of the ideas used in the research are derived from clinical practice and it is usually hoped that the results will, in turn, be found clinically useful.