To Örebro University

Purpose: The aim of this study was to investigate concurrent validity of the Swedish self-rated 36-item World Health Organization Disability Assessment Schedule (WHODAS) 2.0 by comparison with professional Global Assessment of Functioning (GAF) ratings in psychiatric outpatients.

Material and methods: A cross-sectional convenience sample of 444 patients was recruited from their regular psychiatric outpatient settings. The patients filled out the WHODAS 2.0; their clinicians provided clinical information and performed GAF ratings blinded to the patients' assessments. Analyses of correlations, variance components, and ROC curves were performed to investigate the validity of the WHODAS 2.0 through comparison with the GAF. The variance component analyses included working status, psychosocial problems, number of diagnostic groups, and remission status. GAF ratings were separated as total (GAF-T), symptoms (GAF-S), and functioning (GAF-F).

Results: There was significant correlation (p < 0.001) between WHODAS 2.0 total and domain scores and GAF-S, GAF-F, and GAF-T ratings. The correlations varied from r = 0.29 to r = 0.48, with the highest being between GAF-F rating and WHODAS 2.0 total score. Repeating the analyses for separate diagnostic groups replicated the findings, though not for psychotic, substance-related, and eating disorders. The WHODAS 2.0 showed good ability to distinguish impaired functioning below a fixed GAF-T cut-off of 70 (area under the curve: 0.74-0.78). The explained variance was lower for the WHODAS 2.0 than for the GAF (38.9% vs. 59.2%).

Conclusions: Concurrent validity was found when comparing the Swedish self-administered 36-item version of WHODAS 2.0 with the expert-rated GAF in psychiatric outpatients.