Objective: This study examined the construct, discriminant, and incremental validity of scores from the short (SI-S) and long (SI-L) forms of the Symptom Inventory in persons with MS.
Methods: The sample included 133 individuals with MS who completed the SI-L, Performance Scales (PS), EDSS, Multiple Sclerosis Walking Scale-12 (MSWS-12), Multiple Sclerosis Impact Scale-29 (MSIS-29), and Godin Leisure-Time Exercise Questionnaire (GLTEQ) and then wore an accelerometer for 7days. The data were analyzed using SPSS, version 16.0.
Results: There were large correlations between SI-S and SI-L total and subscale scores and between SI-S, SI-L, and PS total scores. The correlations were similar in magnitude between SI-S, SI-L, and PS scores with EDSS and MSIS-29 scores, but not with MSWS-12, accelerometer, and GLTEQ scores. Discriminant function analysis indicated that SI-S scores better differentiated groups with minimal, moderate, and severe disability than did SI-L and PS scores. Regression analysis indicated that SI-S and SI-L scores explained incrementally more variance in EDSS, MSWS-12, and MSIS-29 scores after accounting for PS scores alone.
Conclusion: Such findings provide additional support for the validity of both SI-S and SI-L scores in individuals with MS and support the adoption of either the SI-S or SI-L by clinical MS researchers.