Deriving quality-adjusted life years (QALYs) from constant proportional time tradeoff and risk posture conditions

• Published in: Journal of mathematical psychology 2003-10, Vol.47 (5), p.557-567
• Main Authors: Doctor, Jason N., Miyamoto, John M.
• Format: Article
• Language: English
• Subjects: Conjoint measurement; Decision theory; Health utility analysis; Quality-adjusted life years; Risk; Time tradeoff
• ISSN: 0022-2496; 1096-0880
• DOI: 10.1016/j.jmp.2003.09.001

With foundations in decision theory, Quality-Adjusted Life Years (QALYs) are the most important measure of health outcome in medical decision making. Constant proportional time tradeoff (CP-TTO) is a condition on riskless value with empirical support in the QALY literature. The primary use of CP-TTO in previous axiomatizations of QALYs has been to guarantee that the utility of health state and survival duration is a power function of duration. We show that CP-TTO has other useful applications in QALY research. Under mild conditions CP-TTO implies an additive value function. Furthermore, CP-TTO can be combined with assumptions of risky utility to yield several different parametric QALY representations, including one that is inconsistent with utility independence. We find that CP-TTO simplifies axiomatizations of QALY representations in the sense that if CP-TTO is among the assumptions of a QALY axiomatization, other standard preference assumptions, e.g., double cancellation or utility independence, become redundant and can be dropped from the axiom system. This can be desirable if it allows one to drop from the axiomatization an assumption that is practically difficult to test, e.g., double cancellation.