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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