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Table 3 Rasch model summary statistics of the BIST (overall fit of the scale)

From: Rasch analysis of the Brain Injury Screening Tool (BIST) in mild traumatic brain injury

Analyses Item fit residual Person fit residual Item-trait Interaction PSIa Cronbach’s alpha Unidimensional (sig. t-test % p < 0.05)
(95% CI)
Local dependency
Value SD Value SD χ2 df p   α   
Pathway 1: All 15 items 0.10 0.89 −0.18 1.13 21.67 30 0.87 0.91 0.93 No (> 7) Yes
Pathway 2: Combined Cognitive symptoms subtest
(items 8,9,10,11)
0.26 0.86 −0.11 1.00 26.84 24 0.31 0.90 0.86 No (> 7) Yes
Pathway 3: Three Subtests 0.04 1.13 −0.38 0.97 3.67 6 0.72 0.84 0.77 Yes (4.55) Yes
Subtest 1: Physical-Emotional symptoms (Items 1,2,3,4,12,13,14,15) 0.12 0.97 −0.15 0.88 7.20 16 0.97 0.85 0.88 Yes (4.55) No
Subtest 2: Vestibular-Ocular symptoms (Items 5,6,7) 0.51 0.40 −0.21 0.88 5.46 6 0.49 0.41 0.57 Yes (0.00) No
Subtest 3: Cognitive symptoms (Items 8,9,10,11) 0.19 0.23 −0.33 0.91 1.86 8 0.99 0.83 0.85 Yes (0.91) Yes
Ideal values 0.00 1.0 0.00 1.0    > 0.05b > 0.7   <  5  
  1. SD Standard deviation, χ2 Chi-square, df Degree of freedom, p Probability, PSI Person Separation Index, CI Confidence Interval
  2. a PSI value without extremes; b Bonferroni adjusted