Validation of the Headache Impact Test (HIT-6™) across episodic and chronic migraine

Objective: The purpose of this study was to assess psychometric properties of the six-item Headache Impact Text (HIT-6™) across episodic and chronic migraine. Methods: Using a migraine screener and number of headache days per month (HDPM), participants from the National Survey of Headache Impact (NSHI) study and the HIT-6 validation study (HIT6-V) were selected for this study. Eligible participants were categorized into three groups: chronic migraine (CM: ≥ 15 HDPM); episodic migraine (EM: < 15 HDPM); non-migraine headaches. Reliability and validity of the HIT-6 were evaluated. Results: A total of 2,049 survey participants met the inclusion/exclusion criteria for this study. Participants were identified as 6.4% CM; 42.1% EM; 51.5% non-migraine, with respective mean HIT-6 scores: 62.5 ± 7.8; 60.2 ± 6.8; and 49.1 ± 8.7. High reliability was demonstrated with internal consistency (time1/time2) of 0.83/0.87 in NSHI, and 0.82/0.92 in HIT6-V. Intra-class correlation for test-retest reliability was very good at 0.77. HIT-6 scores correlated significantly (p < .0001) with total Migraine Disability Assessment Scale scores (r = 0.56), headache pain severity (r = 0.46), and HDPM (r = 0.29). Discriminant validity analysis showed significantly different HIT-6 scores (F = 488.02, p < .0001) across the groups. Conclusion: Results from these analyses confirm that the HIT-6 is a reliable and valid tool for discriminating headache impact across episodic and chronic migraine.