Introduction and aims: The aims of this study were to determine the reliability, responsiveness and minimally important change score of the MSIS-29 physical using the EDSS as an anchor measure.
Methods: 214 MS patients (EDSS 0- 8.5) had concurrent MSIS-29 and EDSS assessments at baseline and at up to four years of follow-up.
Results: Stable patients. 116 patients had unchanged EDSS scores. Stability of the MSIS-29 physical (mean change 0.1 points) was better in the 85 patients with EDSS 0 to 5.0 than in the 31 patients with EDSS 5.5 to 8.5 in whom the MSIS-29 physical score fell by eight points, a response shift phenomenon. A floor effect for the MSIS-29 was observed in 5% of stable patients at both time points. Changed Patients. 98 patients experienced EDSS change with moderately strong statistically significant correlations between change scores in the EDSS and the MSIS-29 physical (r = 0.523, p< 0.0001). Effect sizes for MSIS-29 physical change were moderate to large. Using ROC curves, the MSIS-29 change score which produced a combination of optimal sensitivity and specificity was chosen for both EDSS ranges. For EDSS range 5.5- 8, a change score of eight had a sensitivity of 87% and specificity of 67%. For EDSS 0- 5.0, a change score of seven had a sensitivity of 78% and a specificity of 51%.
Conclusions: The MSIS-29 physical performs well over time, and is suitable for use in trials; a minimal change score of eight points in the MSIS-29 is clinically significant.
- disability scales
- multiple sclerosis
- multiple sclerosis impact scale
- response shift
- self-report measures