Assessing validity of the EQ-5D-5L proxy in children and adolescents with Duchenne muscular dystrophy or spinal muscular atrophy

Objective: To assess the psychometric properties of the EuroQol-5-Dimension five-level instrument (EQ-5D-5L) proxy in caregivers of children and adolescents with Duchenne muscular dystrophy (DMD) or spinal muscular atrophy (SMA). Method: Data were collected using the EQ-5D-5L proxy for individuals with DMD or SMA, as reported by their caregivers. Ceiling and floor effects, reliability (Cronbach’s alpha), convergent and divergent validity (Spearman's correlation coefficient and Bland–Altman plot) and known-group validity (analysis of variance) was used to assess the instrument’s psychometric properties. Results: Totally, 855 caregivers completed the questionnaire. Significant floor effects were observed for most dimensions of the EQ-5D-5L in both SMA and DMD samples. The EQ-5D-5L was strongly correlated with the hypothesized subscales of the SF-12, which confirmed satisfactory convergent and divergent validity. The EQ-5D-5L can significantly differentiate between impaired functional groups for individuals, demonstrating satisfactory discriminative ability. The agreement between the EQ-5D-5L utility and EQ-VAS scores was poor. Conclusions: Based on the measurement properties assessed in this study, the EQ-5D-5L proxy is a valid and reliable tool for measuring the health-related quality of life of individuals with DMD or SMA rated by caregivers. Further studies should examine the content validity of the EQ-5D as well as the performance of its young version in these two patient groups.