Objective: Health-related quality of life (HRQoL) is an important outcome measure of migraine treatments. Although a number of migraine-specific HRQoL questionnaires exist, their measurement characteristics have only been examined for patients undergoing acute treatment of migraine. The goal of the current study was to evaluate measurement properties of the widely used Migraine-Specific Quality of Life Questionnaire version 2.1 (MSQ v. 2.1) within a group of patients undergoing prophylactic migraine treatment.
Methods: Various measurement properties of the MSQ were examined in a sample of 916 migraineurs undergoing prophylactic treatment who had scores at baseline and follow-up, as well as baseline SF-36. First, we used confirmatory factor analysis (CFA) and differential item functioning (DIF) to assure the accuracy and stability across groups of the MSQ scoring for all three subscales (Role Restrictive, Role Preventive, and Emotional Functioning). Next, item- and scale-level properties were examined, such as item-total correlations, internal consistency, and convergent and discriminant validity.
Results: Initial findings revealed that item 12 (measuring frustration on the Emotional Functioning subscale) performed poorly. Subsequent to its removal, the 13-item MSQ displayed excellent measurement properties, including stable latent structure at baseline and endpoint, no gender or age biases on items, appropriate item-level and scale-level reliabilities, and markedly higher convergent validity compared to discriminant validity.
Conclusion: The 13-item MSQ appears to be an appropriate measure of migraine-specific HRQoL for patients undergoing migraine prophylaxis. Moreover, given the stability of the latent structure over time, the interpretation of scores is likely to remain quite consistent throughout a clinical trial.