Objective: There is conflicting evidence as to whether depression prevalence is increasing or is stable. Although birth cohort analysis studies show increasing prevalence, longitudinal studies do not. To date there are no published Australian studies providing long-term estimates of depression prevalence. The aim of the present study was to examine the increasing depression prevalence hypothesis in an Australian context.
Method: Data from the 1998 and 2004 South Australian Health Omnibus Surveys were re-analysed. In each survey there were >3000 participants who were interviewed. The data were weighted to achieve representativeness prior to analysis. Depression status was classified by the Primary Care Evaluation of Mental Disorders scale (the PRIME-MD) into major, other and no depressions. Both univariate and multivariable analyses were used to examine depression trends over time and to adjust the data for significant background variables.
Results: There was no significant increase in the cases of patients classified with major depression between 1998 and 2004; there was, however, a significant decrease in other depression. The overall unadjusted prevalence of major depression was 7.4% (6.8% in 1998 and 8.0% in 2004) and for other depression it was 9.5% (10.6% in 1998 and 8.4% in 2004). The highest levels of depression, both major and other, were observed among females aged 15-29 years, and the lowest levels among those aged > or =50 years. The strongest predictor of depression was poor overall health status.
Conclusion: It is time for the conventional wisdom that depression is increasing to be reconsidered, and for a more realistic perspective, developed from evidence-based analyses, to be accepted.