Rasch analysis of UK FIM+FAM in patients with TBI
Table I. The UKROC: trauma brain injury population and the
Rasch random sample characteristics
Age, n (%)
16–40 years
41–65 years
> 65 years
Male, n (%)
Ethnicity, n (%)
White
Asian/Asian British
Black/Black British
Other
Unknown
Length of stay, days, mean (SD)
Diagnosis localization, n (%)
Global/diffuse
Left hemisphere
Right hemisphere
Frontal
FIM+FAM, mean (SD)
Total FIM on admission
Total FAM on admission
Total FIM on discharge
Total FAM on discharge
UKROC
Study sample
n = 1,956 Random sample
(Rasch analysis) a
n = 320
689 (35.2)
830 (42.4)
437 (22.3)
1,466 (74.9) 114 (35.6)
140 (43.8)
66 (20.6)
241 (75.3)
1,463 (74.8)
88 (4.5)
28 (1.4)
138 (7.1)
239 (12.2)
78.2 (68.2) 236 (73.8)
13 (4.1)
5 (1.6)
23 (7.2)
43 (13.4)
77.5 (71.3)
640
480
428
408
(32.7)
(24.5)
(21.9)
(20.9)
66.6 (35.0)
107.7 (52.6)
91.9 (35.5)
149.7 (55.8)
110 (34.4)
65 (20.3)
75 (23.4)
70 (21.9)
68.0 (35.5)
109.5 (53.3)
93.0 (35.7)
151.6 (55.9)
a
Random sample extracted from the dataset (n =
1,956) derived across
admission and discharge values, so that each patient is only in the dataset
once, but both time-points are equally represented.
UKROC: UK Rehabilitation Outcomes Collaborative; SD: standard deviation;
FIM: Functional Independence Measure; FAM: Functional Assessment Measure.
569
30 items were fitted to the Rasch Model without adjustment of
any kind. The second used a super-item approach based on the
method used by Lundgren Nilsson and colleagues (16) to solve
local dependency issues between items of distinct domains.
Locally dependent items were combined into 3 super-items
based on the 3-factor structure identified by steps 1 and 2 above.
In line with our previous analysis in stroke (17), item cali-
brations and DIF were explored across potential person factors
including age group (16–32, 33–49, 50–65, > 65 years), sex, di-
agnosis subcategory (global/diffuse, frontal, left hemisphere, right
hemisphere), and time-point (admission or discharge) and patient
dependency level based on The Northwick Park Dependency
Score (28). The uni-dimensionality of the scale was assessed
using PCA of the residuals (29). This involves comparing person
estimates of the 2 groups of items with highest positive and ne-
gative loadings on the first principal component of residuals after
controlling for the latent Rasch factor using a t-test procedure.
Evidence of uni-dimensionality is obtained if the percentage of
significant t-tests is below 5% or the lower bound of a binomial
confidence interval computed for the number of significant t-tests
overlaps the 5% cut-off point (29). A significance value of 0.05
was used throughout.
RESULTS
The socio-demographic and clinical characteristics of
the Rasch study sample, and the UKROC population
from which it was drawn, are shown in Table I. The
Table II. Principal component loadings after varimax rotation
UK FIM+FAM item
Single component* 2-factor solution
70%
3-factor solution
73%
Variance accounted for: 60% Motor Cognitive Motor
Eating
Swallowing
Grooming
Bathing
Dressing upper body
Dressing lower body
Toileting
Bladder
Bowels
Bed transfers
Toilet transfers
Bath transfers
Car transfers
Locomotion
Stairs
Community mobility
Comprehension
Expression
Reading
Writing
Speech Intelligibility
Social interaction
Emotional status
Adjustment
Leisure activities
Problem solving
Memory
Orientation
Concentration
Safety awareness 0.827
0.763
0.904
0.887
0.897
0.883
0.879
0.832
0.860
0.850
0.847
0.809
0.682
0.810
0.661
0.598
0.762
0.770
0.677
0.670
0.732
0.700
0.586
0.681
0.746
0.768
0.710
0.739
0.762
0.704 0.634
0.550
0.709
0.807
0.789
0.854
0.869
0.747
0.778
0.914
0.915
0.894
0.753
0.880
0.779
0.580 (0.533)
(0.529)
(0.566) 0.703
0.631
0.719
0.788
0.802
0.839
0.868
0.760
0.799
0.900
0.903
0.859
0.610
0.839
0.635
0.408
Cronbach’s alpha 0.976 0.976 0.799
0.780
0.665
0.615
0.606
0.772
0.650
0.814
0.699
0.789
0.812
0.821
0.805
0.752
0.954
Psychsocial
Communication
0.714
0.663
0.832
0.669
0.757
0.813
0.781
0.784
0.779
0.640
0.655
0.759
0.723
0.572
0.976 0.913 0.943
Loadings < 0.5 were suppressed. Pearson Item – total correlations for the single scale were all significant at p < 0.001.
FIM: Functional Independence Measure; FAM: Functional Assessment Measure.
J Rehabil Med 51, 2019