A comparison of directly elicited and pre-scored preference-based measures of quality of life: the case of adhesive capsulitis
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To assess the convergent validity and comparative responsiveness in measuring the health-related quality of life associated with adhesive capsulitis of a disease-specific measure (Shoulder Pain and Disability Index), a generic quality of life measure (SF-36), a preference-based multi-attribute utility scale (assessment of quality of life), and two direct patient preference elicitation methods (willingness to pay and time trade-off).
Instruments administered to all 156 participants in both arms of a randomized placebo-controlled trial of physiotherapy following arthrographic joint distension at baseline were reported at 6, 12, and 26 weeks. Convergent validity was measured using both pooled correlation between instruments and within subjects over time. Responsiveness was measured using the effect size for those with no improvement, moderate improvement, and marked improvement.
With the exception of the monetary measure, all of the instruments showed a low quality of life at baseline with adhesive capsulitis (66– 87 % of perfect health) and a substantial improvement in quality of life to week 26 on recovery. The time trade-off and willingness to pay measures of patient preferences were not responsive to changes in health, but all of the other instruments were at least moderately sensitive to change and moderately correlated with one another.
These findings verify the significant adverse impact of adhesive capsulitis upon quality of life found in larger studies. There was a fair degree of convergence, as measured by the correlation between the instruments but while the time trade-off mean values were quite plausible, at a mean of 87 % of full health before treatment, there was a low correlation with health profile and disease-specific measures. It may be that the time trade-off measured wider aspects of quality of life and that individuals were not prepared to trade survival for potential gains in a self-limiting condition.
KeywordsAdhesive capsulitis Measurement of health-related quality of life Stiff shoulder Time trade-off method Willingness to pay Multi-attribute utility scale
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