Exponential health utility. A characterization and comments on the contribution by Happich and Muhlbacher.

In a recent contribution Happich and Muhlbacher proposed an axiom of constant absolute trade-off of life-years for health states, and studied the family of QALY models satisfying this axiom under expected utility and mutual utility independence between life-years and health states. Here we provide a complete characterization of the family of QALY models satisfying these conditions. This family should not be mistaken for the family of multiplicative exponential QALY models; in particular, it violates the zero condition.