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Table 4 Tests of measurement invariance across country groups

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

HIT-6 item N Percent change in the value of the coefficienta Significance testing for interaction between country and trait level*
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
  1. *P-values <0.0083 (=0.05/6) indicate non-uniform DIF.
  2. aPercent change in the trait level coefficient after removing the country group indicators from the model; values ≥10% indicate uniform DIF.
  3. DF = degrees of freedom; DIF = differential item functioning.