%0 Journal Article %J Quality of Life Research %D 2003 %T Calibration of an item pool for assessing the burden of headaches: an application of item response theory to the Headache Impact Test (HIT) %A Bjorner, J. B. %A Kosinski, M. %A Ware, J. E., Jr. %K *Cost of Illness %K *Decision Support Techniques %K *Sickness Impact Profile %K Adolescent %K Adult %K Aged %K Comparative Study %K Disability Evaluation %K Factor Analysis, Statistical %K Headache/*psychology %K Health Surveys %K Human %K Longitudinal Studies %K Middle Aged %K Migraine/psychology %K Models, Psychological %K Psychometrics/*methods %K Quality of Life/*psychology %K Software %K Support, Non-U.S. Gov't %X BACKGROUND: Measurement of headache impact is important in clinical trials, case detection, and the clinical monitoring of patients. Computerized adaptive testing (CAT) of headache impact has potential advantages over traditional fixed-length tests in terms of precision, relevance, real-time quality control and flexibility. OBJECTIVE: To develop an item pool that can be used for a computerized adaptive test of headache impact. METHODS: We analyzed responses to four well-known tests of headache impact from a population-based sample of recent headache sufferers (n = 1016). We used confirmatory factor analysis for categorical data and analyses based on item response theory (IRT). RESULTS: In factor analyses, we found very high correlations between the factors hypothesized by the original test constructers, both within and between the original questionnaires. These results suggest that a single score of headache impact is sufficient. We established a pool of 47 items which fitted the generalized partial credit IRT model. By simulating a computerized adaptive health test we showed that an adaptive test of only five items had a very high concordance with the score based on all items and that different worst-case item selection scenarios did not lead to bias. CONCLUSION: We have established a headache impact item pool that can be used in CAT of headache impact. %B Quality of Life Research %V 12 %P 913-933 %G eng %M 14661767