Bringing the child's and parents’ voices together: French validation of the SMU and STU quality of life questionnaires in pediatric obesity

Background Childhood obesity is associated with significant impairments in health-related quality of life (HRQoL), yet culturally adapted, weight-specific tools are lacking in French-speaking settings. Aim This study aimed to validate French versions of the Sizing Me Up (SMU) and Sizing Them Up (STU) questionnaires to assess obesity-related quality of life in children and adolescents from self- and parent-report perspectives. Methods Shortened French versions of the SMU and STU were developed, retaining three subscales common to both instruments (Emotional, Physical, and Teasing/Marginalization) based on theoretical and psychometric criteria. A clinical sample included 120 children and adolescents with obesity (aged 5–18 years) and their parents. Psychometric analyses included internal consistency, confirmatory factor analysis, convergent validity with the Pediatric Quality of Life Inventory (PedsQL), sensitivity to body mass index (BMI) z -scores, measurement invariance across age and sex, and parent–child agreement. Results Both instruments demonstrated good internal consistency and a stable three-factor structure. Associations were observed between the BMI z -score and the Physical domain, with modest effect sizes comparable to those of the generic PedsQL. Convergent validity was supported by correlations with corresponding PedsQL subscales. Measurement invariance held across age groups and for the SMU across sex, but the STU across sex did not achieve configural invariance. Procrustean analysis indicated moderate structural similarities between child and parent profiles, with moderate to good individual-level agreement, higher for physical than emotional domains. Summary The shortened French SMU and STU are reliable and valid tools for assessing HRQoL in pediatric obesity, supporting their use in clinical and research settings.