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Table 2 Fit statistics and unidimensionality of the scales

From: Structural validity of the Boston Carpal Tunnel Questionnaire and its short version, the 6-Item CTS symptoms scale: a Rasch analysis one year after surgery

Subscale

Items

Persons

Chi square

DF

P

PSI (extremes/ no extremes)

Percentage (%) of significant t-tests

Location (mean, SD)

Fit residual (mean, SD)

Location (mean, SD)

Fit residual (mean, SD)

     

CTS-6

0.00 (0.69)

-0.14 (1.08)

-2.77 (1.83)

-0.45 (1.18)

15.2

18

0.65

0.73/0.78

5.2

Testlet 1

0.00 (0.75)

0.01 (1.11)

-2.70 (1.77)

-0.39 (1.12)

14.2

15

0.51

0.73/0.79

3.9

Testlet 2

0.00 (0.30)

0.09 (0.45)

-1.51 (1.03)

-0.48 (0.77)

8.5

6

0.20

0.54/0.63

2.0

Symptoms BCTQ

0.00 (0.91)

-0.42 (1.33)

-2.56 (1.99)

-0.42 (1.19)

58.4

33

0.004

0.86/0.88

18.1

Testlets

0.00 (0.10)

-0.10 (0.73)

-0.92 (0.83)

-0.46 (0.74)

18.0

6

0.006

0.86/0.88

2.1

Function BCTQ

0.00 (1.31)

-0.18 (1.10)

-3.51 (1.84)

-0.28 (0.97)

34.8

24

0.07

0.77/0.83

2.5

  1. DF degrees of freedom, P P-value, PSI person separation index, SD standard deviation, CTS-6 The 6-item CTS symptoms scale, BCTQ Boston Carpal Tunnel Questionnaire