PPN6: VALIDATION OF THE 24 HOUR HEADACHE DISABILITY QUESTIONNAIRE (DISQ-24) IN A SAMPLE OF HEADACHE SUFFERERS

Abstract

OBJECTIVES: The Disq-24 was developed to measure headache disability on a 24-hour basis and was first utilized in a sample of migraine subjects who experienced chronic daily headaches. The purpose of this study was to evaluate this instrument's psychometric properties. METHODS: The Disq-24 is a 14-item questionnaire with a 6-point Likert-type scale that measures disability with regards to three hypothesized dimensions: family/social (4-item), work activities (5-item), and emotions/feelings (5-item). This instrument was administered in a prospective, multicenter, randomized, double-blind, placebo-controlled, parallel group trial of 170 transformed migraine sufferers. Four scaling assumptions of summated rating scales (equal variances, equal weights, item-internal consistency and discriminant validity) and scale-level reliability were examined using the baseline data. RESULTS: The means and standard deviations of items within each scale were similar. However, item evaluation demonstrated a floor effect in all items ranging from 22% to 66%. Item internal consistency was generally high and ranged from 0.62 to 0.90. Cronbach's alpha ranged from 0.93 to 0.95 for the three dimensions and was 0.97 for the total score, exceeding the generally acceptable criteria of 0.70. Although each item was highly correlated with the hypothesized scale, the item-scale correlations did not discriminate significantly with other scales. CONCLUSIONS: Although the Disq-24 satisfied the equal variance, equal weights, and internal consistency assumptions of summated rating scales, item discriminant validity was not supported in the above analysis. This lack of support could be due to the small sample size and/or the existence of a unidimensional structure. The validity of the instrument warrants further testing in a headache population which is not restricted to chronic daily headache patients.