Cano S.J.,Clinical Neurology Research Group |
Mayhew A.,Institute of Human Genetics |
Mayhew A.,Newcastle University |
Glanzman A.M.,Children's Hospital of Philadelphia |
And 25 more authors.
Muscle and Nerve | Year: 2014
Introduction: Trial design for SMA depends on meaningful rating scales to assess outcomes. In this study Rasch methodology was applied to 9 motor scales in spinal muscular atrophy (SMA). Methods: Data from all 3 SMA types were provided by research groups for 9 commonly used scales. Rasch methodology assessed the ordering of response option thresholds, tests of fit, spread of item locations, residual correlations, and person separation index. Results: Each scale had good reliability. However, several issues impacting scale validity were identified, including the extent that items defined clinically meaningful constructs and how well each scale measured performance across the SMA spectrum. Conclusions: The sensitivity and potential utility of each SMA scale as outcome measures for trials could be improved by establishing clear definitions of what is measured, reconsidering items that misfit and items whose response categories have reversed thresholds, and adding new items at the extremes of scale ranges. © 2013 Wiley Periodicals, Inc.