Systematic review of the factor structure and measurement invariance of the patient health questionnaire-9 (PHQ-9) and validation of the Portuguese version in community settings

Background: This research sought to review studies that examined the factor structure of the PHQ-9 using a confirmatory factor analysis approach (Study 1); to review studies that tested the measurement invariance of the PHQ-9 (Study 2); to examine the psychometric properties of the European Portuguese version in the general population (Study 3). Methods: Using PRISMA guidelines, a search was performed on Web of Science, PsycINFO, and Scopus from 2001 to August 2019. Assessment of eligibility criteria and data extraction were conducted by two independent researchers (Studies 1 and 2). In Study 3, data were collected from 1479 Portuguese adults, using a cross-sectional design. The BDI-II and the GDS-15 were administered to examine convergent validity. Results: The systematic review identified four-factor models of the PHQ-9 (Study 1). Nineteen studies supported a one-factor model, whereas 12 found evidence for a two-factor model. Both models were supported in general, clinical, psychiatric, and international samples. Study 2 identified ten studies that examined PHQ-9 measurement invariance across 18 groups. The PHQ-9 measurement invariance was fully supported across studies. Study 3 revealed that a two-factor model showed a close fit to data in the European Portuguese version of the PHQ-9. Measurement invariance, reliability, and convergent and divergent validity were also established. Limitations: Study 3 did not include a gold standard measure of depression to evaluate PHQ-9 diagnostic properties. Conclusions: Conceptual implications of the findings are discussed, and recommendations for using the Portuguese version of the PHQ-9 as a screening measure in community settings are also highlighted.