Table 2

Internal and test–retest reliability analysis of the MSSID

Reliability estimatenMobilityFatigueOverall impact
Items included in the factorUnsteadiness or loss of balance. Weakness or heaviness in your legs. Muscle stiffness or spasms. Altered or loss of sensation. Pain. Loss of co-ordination or dexterity. Problems with bladder/bowelFeeling frustrated. Feeling sad or down. Weakness or heaviness in your arms. Fatigue or lack of energy. Difficulties thinking clearly, or forgetting thingsTo what extent did MS stop you from doing what you wanted to do? Compared with what you usually do, how much were you able to do today? On the basis of how your MS has been, how would you describe today? How would you describe your health today?
Cronbach’s alpha590.88–0.900.78–0.880.86
Item−total correlations590.55–0.810.50–0.790.50–0.81
ICC of week 1 and week 4 median scores in stable respondents260.930.790.70
ICC of daily factor scores on first stable consecutive days in each month610.95–0.980.89–0.960.75–0.78