Variability in rates of affective disorders in relatives of depressed and normal probands.

Familial studies of depressed probands vary in the absolute rates of affective disorders in relatives. In a study of 215 mild and severely depressed nonbipolar major depressives and normal probands and 1,331 adult first-degree relatives, attempts were made to account for the sources of variance. The results demonstrated familial aggregation, although degree of aggregation of absolute rates of affective disorders varied among relatives according to the definition of depression used for the relatives, the source of data, and the composition of the relative sample. Despite this variability, the magnitude of the difference in rates between relatives of the normal persons and of the depressed probands remained constant. The rates of affective disorders were always higher in the relatives of the depressed than in the relatives of the normal probands. The magnitude of the difference in rates of depression between the relatives of the depressed subjects and the relatives of the normal probands ranged approximately between twofold and fivefold.