Background: Contemporary clinical trials commonly measure quality of life and medical costs to establish whether therapies are both effective and cost effective. Cost-effectiveness analysis, however, requires a measure of patient utility or preferences for various health states. Because utilities are not often measured directly, we sought to develop a method of translating standard quality-of-life scales into a patient utility measure.
Methods: Five hundred fifty-three patients enrolled in the Bypass Angioplasty Revascularization Investigation Study of Economics and Quality of Life completed a battery of quality-of-life measures and a time trade-off utility assessment an average of 7.3 years after random assignment.
Results: The mean time trade-off score was 8.54 (SD = 2.53) out of a maximum of 10; median score was 9.95. The distribution of scores was skewed, with 12% of patients at the highest possible score of 10. Patients with recurrent angina had significantly lower time trade-off scores than patients without angina (mean 7.03 vs 8.70, P <.05). Time trade-off scores were moderately correlated with each quality-of-life measure (Spearman coefficients 0.38-0.52). Time trade-off scores could be predicted by combinations of 4 (r2 = 0.29), 5 (r2 = 0.31), or 6 (r2 = 0.32) variables.
Conclusions: Time trade-off utility scores can be inferred from commonly used quality-of-life measures. Angina significantly reduces patient utility scores.