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Table 3 Summary fit statistics from Rasch analysis

From: Validation of the Questionnaire to Identify Knee Symptoms (QuIKS) using Rasch analysis

Version Data changes Sample size Item-trait interaction χ2 Item fit residual Person fit residual PSI Significant t-tests
Value (df) P value Mean SD Mean SD
Initial None 145 73.512 (13)* 0.000 0.49 1.84 −0.22 1.18 0.89 7.0
Run 2 Deleted 8 misfit persons 137 72.550 (13) 0.000 0.43 1.93 −0.14 1.01 0.90 5.2
Run 3 Rescored all misfit items 137 19.693 (13) 0.103 −1.01 1.21 −0.66 1.29 0.89 1.6
Run 4a Deleted 20 misfit persons 117 16.105 (13) 0.243 −0.58 1.12 −0.41 1.08 0.90 4.8
Run 5 Formed 4 testlets 117 0.937 (4) 0.92 0.26 0.72 −0.35 0.87 0.84 1.3
Run 6a Used initial data, rescored all items 145 19.480 (13) 0.108 −1.07 1.33 −0.70 1.33 0.89 4.3
Run 7 Formed the 4 testlets again 145 3.546 (4) 0.47 0.02 0.85 −0.45 0.89 0.83 2.9
Run 8 Deleted 1 misfit persons 144 3.612 (4) 0.46 0.03 0.85 −0.43 0.86 0.82 2.9
Rasch-Refined Deleted 3 persons with incomplete data 141 3.613 (4) 0.46 0.00 0.87 −0.44 0.86 0.82 3.0
  1. Criteria of fit to Rasch Model: minimum sample size of n = 108, PSI (Person Separation Index) ≥ 0.80 for reliability assessment by measurement scale, χ2 P-value > 0.05 [Bonferroni-adjusted], Items- and Persons- Fit Residual Mean ~ 0 and SD (Standard Deviation) ~ 1, less than 5 % significant t-test
  2. *Significant after P < 0.05 with Bonferroni correction for the number of items in the analysis
  3. aHad local item dependency