Estimated prevalence of the seasonal subtype of major depression in a Canadian community sample

Objective: To examine estimates of lifetime prevalence of seasonal affectiv e disorder (SAD) in Toronto, Ontario. Method: Random telephone numbers were generated for the city of Toronto, an d 781 respondents completed a telephone interview. Trained nonphysician int erviewers conducted all interviews, which involved structured questions for diagnosing major depression. Patterns of symptom change across seasons wer e evaluated to establish a diagnosis of SAD according to DSM-III-R criteria . Results: Correcting for sex and age, the prevalence of SAD defined by DSM-I II-R criteria was 2.9% (95%CI, 1.7% to 4.0%). and the overall lifetime prev alence of major depression in the sample was 26.4% (95%CI, 23.3% to 29.4%). Some subjects were contacted for a follow-up interview conducted in person ; the positive predictive value for the diagnosis of major depression for t he telephone interview was 100%, and the negative predictive value was 93%. Conclusions: The seasonal subtype of depression represents 11% of all subje cts with major depression, suggesting that SAD is a significant public heal th concern. The telephone interview demonstrated adequate reliability, indi cating that it is appropriate for epidemiological surveys of this nature.