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 improve doctor-patient communication about the functional consequences of migraine. Objectives: To examine the test-retest reliability and internal consistency of the five items and of the overall MIDAS score in population-based samples of migraine sufferers in two countries and to compare consistency across countries. Methods: Using a clinically validated telephone interview, population-based samples of migraine-headache sufferers were identified in the United States (Baltimore, MD) and the United Kingdom (Merton and Sutton, Surrey). Eligible individuals completed the MIDAS questionnaire on two occasions an average of 3 weeks apart. The MIDAS score is derived from five questions about missed time from work and household work (one question each about missed days and days with at least 50% reduced productivity) and missed 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 MIDAS scores were similar between the United States and the United Kingdom. Test-retest Spearman correlations of individual items ranged from 0.46 to 0.78, No significant differences in item-specific correlations were observed between the United States and United Kingdom. The test-retest Pearson correlation of the MIDAS score (i.e., sum of lost days and reduced-effectiveness days in each domain) was 0.80 in the United States and 0.83 in the United Kingdom. The Cronbach alpha, a measure of internal consistency, was 0.76 in the United States and 0.73 in the United Kingdom. Conclusions: This is the first international population-based study to assess the reliability of a disability-related illness severity score for migraine. The reliability and internal consistency of the Migraine Disability Assessment score are similar to that of a previous questionnaire (Headache Impact Questionnaire), However, the Migraine Disability Assessment score requires fewer questions, is easier to score, and provides intuitively meaningful information on lost days of activity in three domains.