extended · article · 2011

Moving towards meaningful measurement: Rasch analysis of the North Star Ambulatory Assessment in Duchenne muscular dystrophy

Anna Mayhew; Stefan Cano; Elaine Scott; Michelle Eagle; Kate Bushby; Francesco Muntoni; David Andrich

AIM: Reliable measurement of disease progression and the effect of therapeutic interventions in Duchenne muscular dystrophy (DMD) require clinically meaningful and scientifically sound rating scales. Therefore, we need robust evidence to support such tools. The North Star Ambulatory Assessment (NSAA) is a promising, clinician-rated scale with potential uses spanning clinical practice and clinical trials. In this study, we used Rasch analysis to test its suitability in these roles as a measurement instrument. METHOD: NSAA data from 191 ambulant boys (mean age at assessment 7 y 8 mo, SD 2 y 4 mo; range 3 y 6 mo-15 y 5 mo) with a confirmed diagnosis of DMD were examined for psychometric properties including clinical meaning, targeting, response categories, model fit, reliability, dependency, stability, and raw to interval-level measurement. All analyses were performed using the Rasch Unidim...