The factor structure of major depression symptoms: a test of four competing models using the Patient Health Questionnaire-9.

Little research has examined the underlying symptom structure of major depressive disorder (MDD) symptoms based on DSM-IV criteria. Our aim was to analyze the symptom structure of major depression, using the Patient Health Questionnaire-9 (PHQ-9). The PHQ-9 was administered to a sample of 2615 Army National Guard soldiers from Ohio. A one-factor model of depression and three separate two-factor models previously established in the literature were evaluated using confirmatory factor analysis. Results demonstrated greater support for the two-factor models of depression than for the one-factor model. The best fitting model was the two-factor model of somatic and non-somatic symptoms supported previously by Krause et al. (2010) and Richardson and Richards (2008). Implications for understanding the components and mechanisms of MDD are discussed.