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Table 1 Summary fit statistics for original and final models for MSIS-29 subscales

From: Rasch analysis of the Multiple Sclerosis Impact Scale (MSIS-29)

Action Analysis Number Overall
model fit
Item fit Mean
(SD)
Person fit Mean
(SD)
PSI % significant t-tests
MSIS-29-PHYS       
Original scale 1 χ2 = 44.04, df = 20, p = .002 .31
(1.46)
-.09
(1.33)
.95  
Rescoring to 3-point 2 χ2 = 21.59, df = 20, p = .36 -.12
(1.29)
-.44
(1.64)
.93  
Removal of 1 case 3 χ2 = 19.34, df = 20, p = .50 -.10
(1.19)
-.44
(1.58)
.93 9.21%
(CI:4–14%)
MSIS-29-PSYCH       
Original scale 4 χ2 = 12.57,
df = 9, p = .18
.09
(1.28)
-.38
(1.58)
.90  
Removal of 1 case 5 χ2 = 14.79,
df = 8, p = .10
.10
(1.31)
-.33
(1.49)
.91 1.69%
  1. PSI = Person Separation Index, SD = standard deviation, df = degrees of freedom, p = probability, CI = confidence interval