Background. Prevalence rates of depression based on the GMS-AGECAT system are markedly higher than rates of major depression diagnosed using DSM-III and DSM-III-R criteria. Interpreting this finding is difficult since AGECAT diagnostic criteria have not been published.

Methods. We conducted a survey in Edmonton, Canada, in which 1119 community residents aged 65 years or older were administered the Geriatric Mental State (GMS) questionnaire. Depression was diagnosed using AGECAT and also according to criteria for DSM-IV major depression and minor depression. We identified 57 items in the GMS relating to major and minor depression which were then grouped into dysphoric, somatic and cognitive categories. The relationship of these symptoms to AGECAT depression was investigated by recoding symptoms to absent (nullifying) and recalculating the number of AGECAT cases. Data were weighted to reflect the underlying population.

Results. There were 143 cases of AGECAT depression (prevalence rate=11·4%), 14 cases of major depression (prevalence rate=0·86%) and 44 cases of minor depression (prevalence rate=3·6%). Of the 154 subjects with either AGECAT or DSM-IV depression, only 47 (31%) were depressed according to both diagnostic systems. Nullifying all dysphoric symptoms reduced the number of AGECAT cases to eight, whereas nullifying somatic and cognitive symptoms reduced the numbers of cases only to 138 and 142, respectively. By themselves, dysphoric symptoms accounted for 77 of the 143 cases of AGECAT depression, while somatic and cognitive symptoms alone accounted for no cases.

Conclusions. AGECAT depression is more inclusive than DSM-IV major or minor depression and AGECAT case status is determined mainly by the proportion of dysphoric symptoms.