Objective: To apply the Rasch measurement model to the development of a clinical tool for measuring manual (dis)ability (ABILHAND). Design: Manual ability was evaluated in terms of the difficulty perceived by a hand-impaired patient on 57 representative unimanual or bimanual activities. Setting: A clinical laboratory. Patients: Eighteen rheumatoid arthritis patients (14 women, 4 men) were interviewed after wrist arthrodesis (10 right, 4 left, and 4 both wrists). Their ages ranged from 38 to 77 years, time since diagnosis ranged from 7 to 41 years, and time since surgery ranged from 0.5 to 17 years. Main Outcome Measure: ABILHAND, administered at a mean duration of 7 years after arthrodesis. Results: Forty-six of the 57 items define a common, single manual ability continuum with widespread measurement range and regular item distribution. Items relating to feeding, grooming, and dressing upper body worked consistently with their counterparts in other disability scales. More difficult items extend the measurement range beyond that of most existing manual ability scales. Conclusion: Even in a small sample of patients, using the Rasch methodology enabled the investigators to produce a useful scale of manual (dis)ability and to define manual ability as a unique construct, at least in patients with rheumatoid arthritis.
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