Psychometric properties of the “Functioning Assessment Scale” in individuals with alcohol and substance use disorder: validity and reliability study

Objective Alcohol and substance use disorders (ASUD) are associated with marked functional impairment, yet brief validated measures of functioning remain limited. This study evaluated the psychometric properties of the Functioning Assessment Scale (FAS) in individuals with ASUD.Methods 180 participants were administered the FAS, a sociodemographic form, the General Assessment of Functioning Scale, the Personal and Social Performance Scale, the Addiction Profile Index–Short Form, and the Clinical Global Impression–Severity scale. Internal consistency, test–retest reliability, convergent validity, known-groups validity, and pre–post changes associated with achievement of early remission were evaluated.Results The FAS showed internal consistency (Cronbach’s α = .96) and test–retest reliability for the total score (ICC = .86, 95% CI [.67, .94]). The FAS total score showed strong positive correlations with GAF and PSP and strong inverse correlations with CGI-S and API, with absolute Spearman correlation coefficients ranging from .79 to .96 (all p < 0.001). FAS domain and total scores differed significantly across clinical phases (all p < 0.001), with lower functioning in the active phase than in remission.Conclusions These findings support the FAS as a brief clinician-rated measure of functioning in ASUD. Its domain-based structure may facilitate individualized rehabilitation planning and longitudinal monitoring of functional recovery in routine treatment settings.