Psychometric Validation of the Generalized Anxiety Disorder Scale (GAD-7) and Patient Health Questionnaire (PHQ-9) in an Inpatient Substance Use Disorder Treatment Program

OBJECTIVE: The Generalized Anxiety Disorder-7 (GAD-7) and Patient Health Questionnaire-9 (PHQ-9) are two widely used instruments for assessing anxiety and depression, respectively, but no studies have examined their psychometric properties among individuals with substance use disorders. This study's objectives were to (a) validate the factor structures, examining single and two-factor models, and (b) examine measurement invariance across age and sex. METHOD: Inpatients with substance use disorders (N = 1,220, 70.9% male, M_age = 41 years) completed the GAD-7 and PHQ-9 as part of routine measurement-based care at admission. Confirmatory factor analysis assessed one-factor and two-factor latent models for the GAD-7 and PHQ-9. RESULTS: Confirmatory factor analysis revealed that in both cases, the one-factor structures exhibited a moderately good fit, with acceptable values for two of four fit indices, but the two-factor structure (with item clusters reflecting cognitive and somatic features) met acceptable fit for all indices. The two-factor models were also invariant across age (examined using quartiles) and sex (female, male). CONCLUSIONS: These findings generally support the psychometric validity of the GAD-7 and PHQ-9 in patients with substance use disorders, but particularly a two-factor model that separates cognitive from somatic features. (PsycInfo Database Record (c) 2025 APA, all rights reserved).