QALYs are by far the most commonly used metric in CEA. A literature survey of cost-effectiveness studies published over 20 years (1981–2000) in the medical and health services research literature identified 328 original CEAs that used a HALY outcome measure. All but one study, which used the healthy year equivalent (HYE) metric, used QALYs (Greenberg and Pliskin, 2002).
The HYE is an economic concept used to determine the number of years in optimal health that would produce the same level of utility for an individual as produced by a lifetime health profile (i.e., a particular succession of health states).
In a critique of the QALY model, Mehrez and Gafni (1990, 1991) proposed alternative approaches for estimating the relative values of alternative health states that do not rely on the strong independence assumptions posited by Pliskin et al. (1980) and the assumption of additivity over time. First, individuals may value two different sequences of health states that result in the same number of QALYs differently. Second, quality and length of life are not valued independently of each other, in contrast to a fundamental assumption of QALYs. Mehrez and Gafni addressed these empirical results by constructing dynamic health profiles extending over the course of life and then eliciting the relative values for these profiles in their entirety with a TTO elicitation technique.
The HYE approach requires comparing a large number of alternative health profiles. Although the HYE has an advantage in that some of the restrictive assumptions associated with QALYs do not apply, preferences must be elicited for specific health profiles, or sequences of health states, rather than for individual health states as with QALYs. Although proponents of the HYE metric contend that the greater methodological demands of the approach are justified in terms of its closer adherence to the theoretical conditions of utility theory, critics counter that developing an empirical base of HYE values for widespread use is not practical. The debate between proponents of QALYs and HYEs boils down to a choice between a simpler model that imposes a smaller information collection burden and a more complex but better fitting model that has demanding and costly data collection requirements.
The DALY is a measure of potential years of life lost to premature death, adjusted to include the equivalent years of healthy life lost through poor health or disability. Box 3-3 provides some background on the origin