Article

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 7y 8mo, SD 2y 4mo; range 3y 6mo-15y 5mo) 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 Unidimensional Measurement Model. Results Overall, Rasch analysis
supported the NSAA as being a reliable (high Person Separation Index of 0.91) and
valid (good targeting, little misfit, no reversed thresholds) measure of
ambulatory function in DMD. One item displayed misfit (lifts head, fit residual
6.9) and there was evidence for some local dependency (stand on right/left leg,
climb and descend box step right/left leg, and hop on right/left leg, residual
correlations >0.40), which we provide potential solutions for in future use of
the NSAA. Importantly, our findings supported good clinical validity in that the
hierarchy of items within the scale produced by the analyses was supported by
clinical opinion, thus increasing the clinical interpretability of scale scores.
Interpretation In general, Rasch analysis supported the NSAA as a
psychometrically robust scale for use in DMD clinical research and trials. This study also demonstrates how Rasch analysis is a useful instrument to detect and
understand the key measurement issues of rating scales.
CI - (c) The Authors. Developmental Medicine & Child Neurology (c) 2011 Mac Keith Press.

Langue : ANGLAIS