The validity of a self-report questionnaire for diagnosing major depressive disorder.

Six hundred thirteen first-degree relatives of schizophrenics, depressives, and normal controls were interviewed with the Diagnostic Interview Schedule (DIS) and completed the Inventory to Diagnose Depression (IDD), a self-report scale to diagnose major depressive disorder (MDD). The current point prevalence of MDD was nearly identical according to the two measures (DIS, 2.8%; IDD, 2.6%). Diagnostic concordance varied according to the Interval between the evaluations. When the two measures were completed within two days of each other the agreement was as high as can be expected between two instruments with less than perfect reliability. We used a family study approach to examine validity and found that both the DIS and IDD cases of depression were two to three times more frequent in the relatives of depressed patients than the relatives of schizophrenics and controls.