Psychometric Properties and Measurement Invariance of the Patient Health Questionnaire 9 in an Italian Coronary Heart Disease Population

Background: Depression is common in patients with coronary heart disease (CHD). The 9-item patient health questionnaire (PHQ-9) is an instrument for screening depression. However, evidence on the psychometric properties of the PHQ-9 in Italian populations with CHD is still lacking. Objective: The objective of this study was to examine the psychometric properties and measurement invariance of the PHQ-9 in a large CHD sample. Methods: This is a secondary analysis of 3-month follow-up data collected from a multicenter longitudinal study. Patients completed a battery of self-reported instruments that included the PHQ-9 and the generalized anxiety disorder scale-7 (GAD-7). Factorial validity was assessed with confirmatory factor analysis. Convergent validity was tested by inspecting the correlations between the PHQ-9 and GAD-7 scores, and other sociodemographic factors. Internal consistency was investigated with the model-based internal consistency reliability index. Measurement invariance was tested across sex and age (≥65 vs <65 years) with confirmatory multigroup factor analysis. Results: We enrolled 427 patients (mean age, 64.41 years; 78.9% male; 66.7% married). The confirmatory factor analysis supported a bi-dimensional factor structure with the factors measuring somatic and cognitive symptoms. Convergent validity testing showed significant positive correlations of the PHQ-9 scores with the GAD-7 scores, gender, and perceived financial status. The model-based internal consistency reliability index was adequate at 0.80. Measurement invariance across age was confirmed at the scalar level, whereas invariance across sex was achieved at the metric level. Conclusion: The PHQ-9 shows adequate psychometric and invariance properties across age groups in patients with CHD. Hence, this instrument can be used in clinical practice and research to assess the severity of depression in patients with CHD and to compare depression scores between younger and older individuals.