Major depression in a nonclinical sample. Demographic and clinical risk factors for first onset.

The relatives, controls, and spouses of affectively ill probands underwent diagnostic examinations on two occasions, 6 years apart. Of 965 subjects who had never been mentally ill when first examined, 11.8% had development of at least one episode of major depression as defined by the Research Diagnostic Criteria during the ensuing 6 years. Subjects younger than 40 years were three times more likely than older subjects to develop depression and women were approximately twice as likely as men to develop depression regardless of age. Marital disruption, a farm setting, and high educational achievement substantially increased the risk of depression among female subjects. Of 214 never-depressed subjects with a history of nonaffective mental disorder, 62 (29.0%) developed major depression. Age and sex were again powerful determinants. The course of prospectively observed secondary depression was more severe than that for primary depression.