The incidence of major depression in Canada: the National Population Health Survey.

OBJECTIVES: To estimate the cumulative incidence of major depressive episode (MDE) over 6 years and the associations between demographic and socioeconomic variables and MDE in a sample of the Canadian national population.

METHODS: Data from the longitudinal cohort of the Canadian National Population Health Survey (NPHS) were used. MDE was assessed using the Composite International Diagnostic Interview - Short Form for Major Depression. Participants of the 2000/01 NPHS were followed until 2006/07. Individuals with previous MDE were excluded from the analysis. Proportional hazard models were developed to assess the associations between demographic, socioeconomic characteristics and MDE.

RESULTS: The cumulative incidence of MDE at 2002/03, 2004/05 and 2006/07 was 2.9% (95% confidence interval: 2.3%, 3.4%), 5.7% (95% confidence interval: 4.9%, 6.4%) and 7.2% (95% confidence interval: 6.4%, 8.1%). Women, youth, participants with one or more chronic medical conditions and those who reported family history of MDE were more likely to have developed MDE. Family history was the strongest risk factor for MDE (hazard ratio=2.01, 95% confidence interval: 1.51, 2.68).

CONCLUSION: It may be valuable for primary and secondary prevention efforts to target women and young people. Family history is an important factor which should be considered in epidemiological studies about major depression, and also can assist in identifying those at high risk of new-onset MDE.