Psychometric validation of the self-administered French version of the Functioning Assessment Short Test (FAST): Factor structure, reliability, validity, and sociodemographic predictors

Background and objectives
The Functioning Assessment Short Test (FAST) is widely used to assess psychosocial functioning across psychiatric conditions. Despite extensive international validation, a validated French version of the self-administered FAST is currently lacking. This study aimed to evaluate the psychometric properties of the self-administered French FAST in a general adult population.
Methods
A total of 508 French-speaking adults aged 18–65 completed the FAST alongside standardized measures of depression and anxiety. Exploratory and confirmatory factor analyses and bifactor modeling evaluated the original six-factor structure. Reliability was assessed using Cronbach’s alpha and McDonald’s omega. Convergent validity was evaluated through multitrait-multimethod (MTMM) analysis and correlations with depression and anxiety. Generalized additive models (GAMs) examined non-linear associations between symptom severity and FAST scores, controlling for demographic covariates.
Results
The original six-factor structure was confirmed, and the bifactor model further supported interpretation of both total and subscale scores. Reliability was strong for the total FAST score (α = .86; ω = .90), whereas subscale reliability (α = .58–.80), with lower values for autonomy, cognitive, and leisure. MTMM analysis demonstrated moderate-to-high monotrait correlations (.51–.84), and moderate correlations with depressive (r = .46) and anxiety (r = .35) symptoms, supporting convergent validity. GAM analyses revealed a non-linear relationship between depressive symptoms and psychosocial impairment (edf = 2.91, F = 19.87, p < .001), alongside significant effects of anxiety (p = .024) and employment status (p = .003).
Conclusions
The French self-administered FAST demonstrates robust psychometric properties and appears suitable for assessing psychosocial functioning in general adult populations, though caution is advised when interpreting autonomy, cognitive, and leisure subscales in non-clinical samples until further clinical validation is available.