Objective: To compare the measurement properties of the HAQ disability index (HAQ-DI), HAQ-II and short form 36 physical functioning scale (PF-10) in patients with gout.
Methods: A cross-sectional sample of 97 patients with gout completed all three measures. Reliability was assessed by examining the internal consistency of the scales. Validity was assessed by testing for expected intercorrelations and associations with other aspects of health status and the ability to discriminate between patients with different levels of general health. Additionally, distributional properties were examined.
Results: All three measures demonstrated high reliability (Cronbach's α ≥ 0.93), strong intercorrelations (r ≥ 0.75), and the expected pattern of external correlations. The HAQ-DI and HAQ-II performed somewhat better in discriminating between patients. However, both demonstrated ceiling effects of 34.0 and 25.8%, respectively, compared with only 7.2% of the patients scoring no disability on the PF-10.
Conclusions: The HAQ-DI, HAQ-II and PF-10 demonstrated similar and adequate reliability and validity for measuring functional disability in patients with gout. The large ceiling effects of both HAQ versions, however, may point to limited content validity and responsiveness to change. Further research should examine whether current instruments cover all aspects of physical functioning relevant to patients with gout.