Reliability and validity of the 6-item Headache Impact Test in chronic migraine from the PROMISE-2 study
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Reliability and validity of the 6‑item Headache Impact Test in chronic migraine from the PROMISE‑2 study Carrie R. Houts1 · James S. McGinley1 · R. J. Wirth1 · Roger Cady2 · Richard B. Lipton3 Accepted: 3 October 2020 © The Author(s) 2020
Abstract Purpose We examined the reliability and validity of the 6-item Headache Impact Test (HIT-6) specifically on patients with chronic migraine (CM) from the PROMISE-2 clinical trial. Methods The conceptual framework of HIT-6 was evaluated using baseline data from the PROMISE-2 study (NCT02974153; N = 1072). A unidimensional graded response model within the item response theory (IRT) framework was used to evaluate model fit and item characteristics. Using baseline and week 12 data, convergent and discriminant validity of the HIT-6 was evaluated by correlation coefficients. Sensitivity to change was assessed by evaluating correlations between HIT-6 scores and change scores for other established reference measures. All examined correlations were specified a priori with respect to direction and magnitude. Known-groups analyses were anchored using Patient Global Impression of Change and monthly headache days at week 12. Results A unidimensional model fit the data well, supporting that the 6 items measure a single construct. All item slopes and thresholds were within acceptable ranges. In both the validity and sensitivity to change analyses, all observed correlations conformed to directional expectations, and most conformed to magnitude expectations. Known-groups analyses demonstrated that the HIT-6 total score can distinguish between clinically meaningful CM subgroups. Conclusion The HIT-6 was successfully calibrated using IRT with data from PROMISE-2. Results from these analyses were generally consistent with previous literature and provided supportive evidence that the HIT-6 is well suited for measuring the impact of headache and migraine in the CM population. Keywords HIT-6 · Construct validity · Chronic migraine · Item response theory · PROMISE-2
Introduction Chronic migraine (CM) is a common neurological disorder defined as having 15 or more headache days per month for more than 3 months with at least 8 days per month having features of migraine with or without aura [1]. Previous research has shown associations between CM and increased headache impact and disability as well as decreased healthrelated quality of life (HRQoL) [2–5]. Migraine is associated
* Carrie R. Houts [email protected] 1
Vector Psychometric Group, LLC, Chapel Hill, NC, USA
2
Lundbeck Seattle BioPharmaceuticals, Inc, Bothell, WA, USA
3
Department of Neurology, Albert Einstein College of Medicine, Bronx, NY, USA
with increased familial burden and elevated direct and indirect medical costs [6–9], as well as increased occurrence of fatigue, irritability, headache pain severity, and comorbidities [10–12]. Preventive treatments for migraine are intended to decrease the frequency and impact of migraine attacks. A typical endpoint in migraine prevention trials is the mean change in mo
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