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

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.