From: Exploring differential item functioning in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)
Sub-group
DIF items using each criteria
Type of DIF (SRbon)
Impact (p value)
SR
SRbon
t-tests
Effect size change
Age
2, 4
2
U(+)
0.007
<0.0005
Social Class
3 (5)
Employed
2,3,4, 5
2,3
BMI
4
U and NU
0.0005
0.15