Psychometric properties of quick disabilities of the arm, shoulder, and hand questionnaire among people with carpal tunnel syndrome: item response theory analysis

The objective of this retrospective cross-sectional register-based study among 1597 patients with electromyography-confirmed carpal tunnel syndrome (CTS) was to evaluate the psychometric properties of the quick disabilities of the arm, shoulder, and hand questionnaire (QuickDASH). Two-parameter item response theory analysis with a rating scale model was applied. Of the respondents, 896 (56%) were women. The average age was 55.0 (SD: 16.3) years. Mean QuickDASH score was 38.0 (SD: 23.2%) points. For difficulty parameter estimates, some items demonstrated a slight shift to the right toward higher QuickDASH scores. The intervals between the difficulty estimates across all scoring options were highly similar, exhibiting only minor fluctuation. Overall, the test characteristic curve for the entire QuickDASH showed a slight shift toward worse disability and higher scores. Item discrimination estimates ranged from moderate 1.20 to perfect 3.31. For 9 out of 11 items, the discrimination estimates were perfect, that is, greater than 1.7. Overall, QuickDASH demonstrated consistent difficulty across item response options and good ability to differentiate between respondents with varying degrees of functional limitations. In other words, QuickDASH in this sample proved to be a measure that was well able to distinguish patients at different levels of functional limitations caused by CTS. A modest shift toward higher disability levels was observed for most of the items and for the overall scale, suggesting that patients might tend to underestimate their disability severity assessed by QuickDASH. However, this shift was so mild that it would hardly be of any significance in a typical clinical situation.