PHQ-9: One factor or two?

Area of Science:

• Psychometrics
• Mental Health Assessment
• Scale Analysis

Background:

• The Patient Health Questionnaire (PHQ-9) is a widely used depression screening tool.
• Previous research suggests both one-factor and two-factor structures for the PHQ-9.
• The psychometric properties of the PHQ-9 have not been fully explored using Mokken scale analysis.

Purpose of the Study:

• To investigate the psychometric properties of the PHQ-9 using Mokken scale analysis.
• To compare the fit of one-factor and two-factor models for the PHQ-9.
• To determine the most appropriate factor structure for the PHQ-9.

Main Methods:

• Confirmatory Factor Analysis (CFA) was used to assess model fit.
• Mokken scale analysis was employed to evaluate the unidimensionality of the PHQ-9.
• Retrospective data from an NHS Trust was utilized for the analyses.

Main Results:

• Confirmatory Factor Analysis indicated a two-factor structure provided a significantly better fit.
• However, the factors identified in the CFA were highly correlated.
• Mokken scale analysis suggested that a single-factor model is viable for the PHQ-9.

Conclusions:

• The findings support recent research indicating a one-factor model is most appropriate for the PHQ-9.
• A single-factor structure may better represent the underlying construct of depression measured by the PHQ-9.
• Further psychometric investigation using Mokken analysis confirms the utility of the PHQ-9.