Validation of the Headache Impact Test (HIT-6) in patients with chronic migraine

Table 4 Tests of measurement invariance across country groups

HIT-6 item		N	Percent change in the value of the coefficient^a	Significance testing for interaction between country and trait level*
HIT-6 item		N	Percent change in the value of the coefficient^a	Wald chi-square	DF	P-value
A	Pain Severe When Headache	1,375	0.2	5.187	2	0.0747
B	Limit Ability to Do Daily Acts	1,376	2.8	6.402	2	0.0407
C	Wish Could Lie Down	1,376	2.2	1.847	2	0.3971
D	Too Tired to Do Work or Daily Acts	1,376	0.1	1.241	2	0.5377
E	Feel Fed Up/Irritated Because of Headache	1,375	7.8	2.243	2	0.3258
F	Limit Ability to Concentrate	1,376	1.4	2.362	2	0.3070

*P-values <0.0083 (=0.05/6) indicate non-uniform DIF.
^aPercent change in the trait level coefficient after removing the country group indicators from the model; values ≥10% indicate uniform DIF.
DF = degrees of freedom; DIF = differential item functioning.

ISSN: 1477-7525