Background: In contrast to the huge number of prevalence studies, there are relatively few incidence studies of depressive disorders. Furthermore, estimates of incidence vary remarkably between existing studies. The aim of this paper is to add knowledge about the incidence and determinants of depressive disorder, based on the Finnish sub-sample of the European Outcomes of Depression International Network study.
Method: The random population sample in the Finnish sub-study consisted of 2,999 subjects, aged 18-64, selected from one urban and one rural area. In the baseline survey, potential cases of depressive disorder were identified using the Beck Depression Inventory. SCAN-2 interview was used to assign caseness against ICD-10 criteria. Findings from the 1-year follow-up survey with those who responded in the baseline survey (N=1,939), using the same case-finding instruments, were used to estimate the incidence rate of depressive disorder.
Results: The estimated annual incidence rate for all depressive disorders, including both first-time and recurrent episodes, was 28.5 per 1,000; for first-time episodes it was 20.5 per 1,000. Significant predictors for experiencing a depressive episode were: suffering from self-perceived long-term illness or handicap, experiencing little or no concern from friends, low sense of coherence, low self-confidence, uncertainty about one's future and reporting two or more threatening life events during the preceding 6 months.
Conclusions: About 3% of the working-age population experience an episode of depressive disorder each year. Due to recall problems, the estimate of first-time incidence may be too high.