Validation of the PHQ-9 in a psychiatric sample

Area of Science:

• Psychiatry
• Psychometrics
• Mental Health Assessment

Background:

• The Patient Health Questionnaire-9 (PHQ-9) is widely used in primary care but its utility in psychiatric populations is less understood.
• This study investigates the PHQ-9's psychometric properties as a severity measure for diverse psychiatric disorders.

Purpose of the Study:

• To comprehensively validate the PHQ-9 in a large psychiatric sample.
• To assess its performance as a severity measure, treatment outcome measure, and screening tool for depressive episodes.

Main Methods:

• 1023 patients completed the PHQ-9 at admission and discharge, alongside other self-report measures and a structured diagnostic interview.
• Exploratory and confirmatory factor analyses were used to examine the PHQ-9's factor structure.

Main Results:

• The PHQ-9 demonstrated good internal consistency (α=.87) and strong correlations with depression measures.
• It showed good sensitivity to change, with a large pre- to post-treatment effect size.
• A cut-off of ≥13 showed good sensitivity (.83) and specificity (.72) for screening depressive episodes. A two-factor solution emerged from factor analysis.

Conclusions:

• The PHQ-9 is a validated measure for assessing depression severity and treatment outcomes in psychiatric patients.
• It performs well as a screener for current depressive episodes, potentially with a higher recommended cut-off for psychiatric samples.
• Limitations include the absence of clinician-rated improvement measures and limited ethnoracial diversity in the sample.