Deriving a preference-based measure for people with Duchenne Muscular Dystrophy from the DMD-QoL

Objective: This study generates a preference-based measure for capturing the quality of life of people with Duchenne muscular dystrophy (DMD) from a new measure of quality of life, DMD-QoL. Methods: A health state classification system was derived from the DMD-QoL based on psychometric performance of items, factor analysis and item response theory analysis. Preferences for health states described by the classification system were elicited using an online discrete choice experiment (DCE) survey with life years as an additional attribute, from members of the UK general population (n=1,043). DCE data was modelled using a conditional fixed-effects logit model and utility estimates were directly anchored on the 1-0 full health-dead scale. Results: The health state classification system has 8 dimensions: mobility; difficulty using hands; difficulty breathing; pain; tiredness; worry; participation; feeling good about yourself. The standard model had mostly statistically significant coefficients and reflected the instrument’s monotonic structure. However, two dimensions had inconsistent coefficients (where utility increased as health worsened) and a consistent model was estimated that merged adjacent inconsistent severity levels. The best state defined by the classification system has a value of 1 and the worst state has a value of -0.559). Conclusions: The modelled results enable DMD-QoL-8D utility values to be generated using DMD-QoL or DMD-QoL-8D data in order to generate QALYs for people with DMD. QALYs can then be used to inform economic models of the cost-effectiveness of interventions in DMD. Future research comparing the psychometric performance of DMD-QoL-8D to existing generic preference-based measures, including EQ-5D-5L, is recommended.