An international study to assess reliability of the Migraine Disability Assessment (MIDAS) score

Background: The Migraine Disability Assessment (MIDAS) instrument is a five -item questionnaire developed to measure headache-related disability and im prove doctor-patient communication about the functional consequences of mig raine. Objectives: To examine the test-retest reliability and internal cons istency of the five items and of the overall MIDAS score in population-base d samples of migraine sufferers in two countries and to compare consistency across countries. Methods: Using a clinically validated telephone intervie w, population-based samples of migraine-headache sufferers were identified in the United States (Baltimore, MD) and the United Kingdom (Merton and Sut ton, Surrey). Eligible individuals completed the MIDAS questionnaire on two occasions an average of 3 weeks apart. The MIDAS score is derived from fiv e questions about missed time from work and household work (one question ea ch about missed days and days with at least 50% reduced productivity) and m issed days of nonwork activities. Results: A total of 97 migraine-headache sufferers from the United States and 100 from the United Kingdom completed the MIDAS questionnaire twice. Mean and median item values and overall MIDA S scores were similar between the United States and the United Kingdom. Tes t-retest Spearman correlations of individual items ranged from 0.46 to 0.78 , No significant differences in item-specific correlations were observed be tween the United States and United Kingdom. The test-retest Pearson correla tion of the MIDAS score (i.e., sum of lost days and reduced-effectiveness d ays in each domain) was 0.80 in the United States and 0.83 in the United Ki ngdom. The Cronbach alpha, a measure of internal consistency, was 0.76 in t he United States and 0.73 in the United Kingdom. Conclusions: This is the f irst international population-based study to assess the reliability of a di sability-related illness severity score for migraine. The reliability and i nternal consistency of the Migraine Disability Assessment score are similar to that of a previous questionnaire (Headache Impact Questionnaire), Howev er, the Migraine Disability Assessment score requires fewer questions, is e asier to score, and provides intuitively meaningful information on lost day s of activity in three domains.