Psychometric evaluation of the PROMIS parent proxy mobility item bank for use in Duchenne muscular dystrophy

Abstract Aim To evaluate the psychometric properties and measurement quality of the Patient‐Reported Outcomes Measurement Information System Parent Proxy (PROMIS PP) Mobility item bank (v1.0, 23 items) for children with Duchenne muscular dystrophy (DMD), through Rasch statistical analysis. Method De‐identified PROMIS PP Mobility items were completed by the caregivers of male patients with DMD, aged 4 to 12 years, as part of standard clinical care at the Nationwide Children's Hospital clinic; data were mined retrospectively from electronic health records. Rasch analysis was used to assess the internal functioning of the measure and items. Results Overall, 151 observations were available for the Rasch analysis, equally split between patients aged 4 to 7 years and 8 to 12 years. After removing clinically irrelevant items and regrouping response options for specific items, the resulting 19‐item measure demonstrated overall good fit to Rasch model expectations and the ability to discriminate between respondents with different mobility levels (Person Separation Index = 0.95, excellent reliability). Interpretation The customized PROMIS PP Mobility measure demonstrated good fit and may be a reliable option for mobility assessment in children with DMD. Rasch analysis can be used by other researchers to improve the sensitivity of patient‐reported outcomes in their field of interest.