Major Depression Prevalence in Calgary
Scott B Patten, MD, FRCPC, PhD1
Objective: To estimate the 12-month period prevalence of major depression in Calgary.
Method: Subjects (n = 2542) were selected using random digit dialing (RDD) and interviewed by telephone using the Composite International Diagnostic Interview-Short Form for Major Depression (CIDI-SFMD). A subset of this sample was recontacted and administered the full mood disorders section of the CIDI.
Results: The weighted proportion of the sample scoring in the positive range on the major depression predictor was 14.7%. Validation data determined that approximately three-quarters of these subjects would be expected to have major depression according to the CIDI. Hence, the estimated 12-month period prevalence of major depression was approximately 11.0%.
Conclusion: This prevalence estimate is higher than most, but not all, previous Canadian estimates and resembles that of the American National Comorbidity Survey (NCS). Calgary may have a high prevalence of major depression; however, because methodologically comparable studies are not available, to conclude this would be premature. Selection bias due to the RDD sampling (and the associated relatively high rate of nonresponse) may have led to an inflated prevalence estimate. Alternatively, because it allows increased anonymity and emotional “distance” from the nonprofessional interviewers, telephone-based data collection may be more sensitive to psychopathology than face-to-face interviewing.
(Can J Psychiatry 2000;45:923-926)
Key Words: major depression, depressive disorder, epidemiological studies, prevalence, cross-sectional studies
Estimates of major depression prevalence have varied considerably across different studies. Often, these differences have been attributed to different measurement strategies (1). Yet, even when methodologically homogeneous studies are compared, considerable variability among populations has been reported. For example, a recent review of studies using methods resembling those employed in the American Epidemiological Catchment Area (ECA) project found that 12-month prevalence rates for major depression varied from 0.8% in Taiwan to 5.2% in Paris. A lifetime prevalence of 1.5% was reported in Taiwan, and a 19.0% lifetime rate was reported in Beirut (2).
Some recent data suggest a higher prevalence of major depression in the US than in Canada. The National Comorbidity Survey (NCS), which used a University of Michigan modification of the CIDI (UM-CIDI) reported a 12-month period
received October 1999, revised, and accepted June 2000.
prevalence of 10.3% (3). The mental health supplement of the Ontario Health Survey used the same instrument and reported a 4.1% prevalence (4). However, an annual prevalence of 10.4% was found in a Metropolitan Toronto sample (5). This paper reports a 12-month major depression period prevalence estimate for Calgary.
Data collection for this study took place between February 1, 1998, and July 1, 1999. The sample was selected by random digit dialling (RDD). The target population consisted of adults aged 18 years or more who were residents of telephone-containing households in Calgary, and the sampling frame included all working residential numbers in the city. Telephone numbers were randomly generated using an application of the Mitofsky-Waksberg method (6), with a modification attributed to Waksberg and described in a review by Potthoff (7). The modification involved random generation of a set of 10 phone numbers from each sampling “block,” rather than the traditional Mitofsky-Waksberg approach of repeated second-stage calling until a preset number of interviews were completed. When a residential household was reached, one member of the household was selected according to the most recent birthday.