TY - JOUR T1 - Calibration of an item pool for assessing the burden of headaches: an application of item response theory to the Headache Impact Test (HIT) JF - Quality of Life Research Y1 - 2003 A1 - Bjorner, J. B. A1 - Kosinski, M. A1 - Ware, J. E., Jr. KW - *Cost of Illness KW - *Decision Support Techniques KW - *Sickness Impact Profile KW - Adolescent KW - Adult KW - Aged KW - Comparative Study KW - Disability Evaluation KW - Factor Analysis, Statistical KW - Headache/*psychology KW - Health Surveys KW - Human KW - Longitudinal Studies KW - Middle Aged KW - Migraine/psychology KW - Models, Psychological KW - Psychometrics/*methods KW - Quality of Life/*psychology KW - Software KW - Support, Non-U.S. Gov't AB - 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. VL - 12 N1 - 0962-9343Journal Article ER -