Under a CBA–CEA link, Conditions 1 through 4 require that the marginal utility of
consumption does not change in response to a change in health status, so that Condition 5
cannot also hold (for a proof of this, see Appendix B). Where Condition 5 holds then theWTP
for a given health improvement will necessarily be greater for those in poor health where
utility is less sensitive to consumption. For a QALY to have a monetary value that holds
for all individuals across society, we must restrict the utility function so that consumption
and health are linearly separable in the utility function. In addition, utility must be a linear
function of these factors, since any non-linearity will cause the WTP-per-QALY to vary
according to the initial levels of health and consumption.