Prevalence, impairment and severity of 12-month DSM-IV major depressive episodes in Te Rau Hinengaro: New Zealand Mental Health Survey 2003/4

Objective: To assess the prevalence, symptom severity, functional impairment and treatment of major depressive episodes in the New Zealand population, in light of recent criticism that depression is ‘over-diagnosed’, especially in community surveys. Method: Nationally representative cross-sectional household survey of 12 992 adults (aged 16+): The New Zealand Mental Health Survey 2003/4. 12-month major depressive episode measured in face-to-face interviews with the Composite International Diagnostic Interview (CIDI 3.0). Results: The 12-month prevalence of major depressive episode (MDE) was 6.6% for the total population, with decreasing prevalence with increasing age, and higher prevalence in females (8.1% versus 4.9% in males). Fewer than 10% of 12-month episodes were classified on a symptom severity rating scale as mild, and 69% of all episodes were accompanied by severe impairment in at least one domain of functioning. Only a third of those with severe impairment received treatment in the mental health sector, and half saw a general medical practitioner. Conclusion: These results offer little support for the suggestion that depression is over-diagnosed and over-treated, and that current diagnostic thresholds allow the inclusion of too many mild episodes in community surveys.