INCIDENCE OF MENTAL-DISORDERS IN EDMONTON - ESTIMATES OF RATES AND METHODOLOGICAL ISSUES

An incidence study was conducted in Edmonton, Alberta, Canada, in whic h 3956 community residents were interviewed using the Diagnostic Inter view Schedule (DIS) and a sample of 1964 subjects were reinterviewed w ith the DIS an average of 2.8 years later. Incidence rates, estimated for a range of DSM-III disorders, were surprisingly large, raising que stions about the reliability of DIS data. We examined major depression in detail to uncover possible sources of unreliability. There were 13 8 'incident' cases of major depression, giving an annual incidence rat e for both sexes of 27.9 (per 1000). However, based on reinterview dat a, 106 (80%) of the incident cases reported an age of onset prior to t he initial interview. These findings appear to be the result of a diff erence between the DIS definition of age of onset and the one used in our analysis of incidence. A syndrome called depressive spell is defin ed and used to demonstrate that the large number of incident cases is likely due, at least in part, to incomplete recall of lifetime depress ive symptoms. Despite these potential sources of bias, the possibility remains that incidence rates and lifetime risks in Edmonton are large r than has generally been reported in the literature. (C) 1998 Elsevie r Science Ltd. All rights reserved.