An exponential representation of health state utility.

It has been shown which assumptions are reasonable to combine quality of life with length of life, those attributes fundamental to the quality-adjusted life-year concept. One of these assumptions is the so-called "constant proportional tradeoff" which restricts the underlying utility functions for life-years to those consistent with constant proportional risk posture. However, this might be too restrictive because "constant absolute tradeoff" cannot be reflected. Pliskin et al. mentioned this case already and suggested an exponential function as a proper function to reflect the underlying constant absolute risk posture. Its proof is given in the appendix of this article. A survey among tinnitus patients, however, shows that this assumption is less plausible. Further research is needed to confirm that finding.