Examining the unidimensionality of the PHQ-9 with first responders: Evidence from different psychometric paradigms.

The Patient Health Questionnaire-9 (PHQ-9) is an effective tool for identifying depressive disorders in diverse populations, making it a valuable resource in both clinical practice and research. However, the factor structure and dimensionality of the instrument have been contested. Studies have raised questions about whether the PHQ-9 adequately captures a single underlying construct or reflects multiple distinct dimensions of depression. This study examines the factor structure of the PHQ-9 among South African first responders using exploratory factor analysis (EFA), confirmatory factor analysis (CFA) with ancillary bifactor indices, parallel analysis and Mokken analysis. A cross-sectional study design was used with data collected from police officers (n = 309) and paramedics (n =120). Although the EFA identified a two-factor structure, this was not supported by the other analyses. While the one-factor, correlated two-factor and bifactor models of the PHQ-9 had comparable fit indices, the one-factor model appeared to be marginally superior in the CFA. Ancillary bifactor and parallel analysis also did not support the interpretation of the PHQ-9 as multidimensional. Lastly, Mokken scale analysis confirmed that the PHQ-9 is a strong and reliable unidimensional scale of depression. These findings suggest that the PHQ-9 predominantly measures a single construct of depression, consistent with the unidimensional view of the disorder.

Pubmed ID: 40406659