Abstract
This paper investigates the theoretical properties of healthy-years equivalents (HYEs) and quality-adjusted life-years (QALYs). A distinction is made between ex ante HYEs (EA-HYEs) and expected HYEs (EXP-HYEs) and between risk-neutral quality-adjusted life-years (RN-QALYs) and risk-adjusted quality adjusted life-years (RA-QALYs). In the case of certainty, HYEs always rank health profiles according to individual preferences, whereas QALYs only rank health profiles according to individual preferences if constant proportional trade-off holds for all health states and if additive independence of quality in different periods holds. In the case of uncertainty, EA-HYEs always rank risky health profiles the same way as expected utility. The assumptions needed for the other measures to rank risky health profiles the same way as expected utility are: risk neutrality with respect to healthy time for EXP-HYEs; risk neutrality with respect to time in all health states and additive independence of quality in different periods for RN-HYEs; and constant proportional risk posture with respect to time in all health states and additive independence of quality in different periods for RA-QALYs.