Validation of the <scp>QOLIBRI</scp> ‐ <scp>KIDDY</scp> self‐rated and proxy‐rated questionnaires after paediatric traumatic brain injury

AIM: To conduct a psychometric validation and to evaluate the clinical relevance of the Quality of Life after Brain Injury in children aged 6 to 7 years (QOLIBRI-KIDDY) self-reported and proxy- or parent-reported questionnaires for traumatic brain injury (TBI)-specific health-related quality of life (HRQoL). METHOD: One hundred and seven parent-child dyads completed the QOLIBRI-KIDDY, generic HRQoL, and symptom assessments. Analyses examined internal consistency, test-retest reliability, factorial structure, construct and known-group validity, and International Classification of Functioning, Disability and Health (ICF) item linking. RESULTS: Both versions demonstrated good-to-excellent total score internal consistencies (Cronbach's α and McDonald ω > 0.8) and acceptable-to-good subscale consistencies (0.34-0.79). Acceptable (proxy) to good (self) test-retest reliability (intraclass correlation coefficient = 0.60-0.73) and a 6-scale structure (cognition, self, daily life and autonomy, social relationships, emotions, physical problems) was found. TBI-specific HRQoL correlated moderately to strongly with generic health status (self-report Pearson's r = 0.57; parent-report r = 0.71). Poorer proxy-report HRQoL was associated with more health problems, anxiety, depression, and more severe TBI, with medium-to-large effects (Cohen's d = 0.45-1.28). Items were mapped to 27 two-level ICF categories. INTERPRETATION: Both instruments are reliable and valid, enabling TBI-specific HRQoL assessment over the lifespan. Identifying the subjective meaning of disability by covering key ICF domains assists early impairment detection, planning of individualized care, and prevention of long-term adverse outcomes.