Psychometric properties for the physical and psychological MSIS-29 impact scales
| Psychometric property | MSIS-29 physical | MSIS-29 psychological | ||
|---|---|---|---|---|
| ICC, intraclass correlation coefficient; MSIS-29, Multiple Sclerosis Impact Scale. | ||||
| Data quality | ||||
| Item missing data | 0.5% | 0.1% | ||
| Computable scale scores | 93.5% | 98.4% | ||
| Item test–retest reliability (ICC) | 0.87 | 0.83 | ||
| Scaling assumptions | ||||
| Item mean scores range | 2.1 to 3.3 | 1.8 to 2.9 | ||
| Item SD range | 1.0 to 1.5 | 1.1 to 1.4 | ||
| Item skewness range | −0.499 to +0.742 | 0.201 to +1.235 | ||
| Item-total correlation range | 0.55 to 0.85 | 0.41 to 0.86 | ||
| Acceptability | ||||
| Observed scale score range | 0 to 91.3 | 0 to 91.7 | ||
| Scale score (mean (SD)) | 43.9 (24.2) | 32.7 (23.2) | ||
| Floor/ceiling effect (%) | 4.7/1.6 | 1.6/1.6 | ||
| Skewness | −0.231 | 0.459 | ||
| Reliability | ||||
| Cronbach’s α | 0.96 | 0.90 | ||
| Scale test–retest reliability (ICC) | 0.87 | 0.83 | ||
| Responsiveness | ||||
| Correlation | 0.07 | 0.24 | ||
| Effect size | 0.05 | 0.02 | ||
| Clinically important difference: | ||||
| improved patients (n = 30) | 0.6 | 0.8 | ||
| deteriorated patients (n = 7) | 0.2 | 1.1 | ||