Background: The nine-item depression module from the Patient Health Questionnaire (PHQ-9) is widely used as an open access screening instrument for depression in different health care and community settings; thus far, normative data from the general population are still scarce. The objectives of the study were to generate normative data and to further investigate the construct validity and factor structure of the PHQ-9 in the general population.
Methods: Nationally representative face-to face household surveys were conducted in Germany between 2003 and 2008 (n=5018). The survey questionnaires included the PHQ-9, the Satisfaction with Life Scale, the 12-item Short Form Health Survey (SF-12) for the measurement of health-related quality of life and demographic characteristics.
Results: Normative data for the PHQ-9 were generated for both genders (53.6% female) and different age levels [mean age (S.D.) of 48.9 (18.1) years]. Women had significantly higher mean (S.D.) scores compared with men [3.1 (3.5) vs. 2.7 (3.5)]. A prevalence rate of moderate to high severity of depressive symptoms of 5.6% was identified. Intercorrelations with depression were highest for the Mental Component Scale of the SF-12, followed by the Physical Component Scale of health-related quality of life, and life satisfaction. Results supported a one-factor model of depression.
Conclusions: The normative data provide a framework for the interpretation and comparisons of depression with other populations. Evidence supports reliability and validity of the unidimensional PHQ-9 as a measure of depression in the general population.
Keywords: Depressive symptoms; Epidemiology; Factor structure; Normative data; Screening.
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