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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