A test of the QALY model when health varies over time.

Quality-adjusted life years (QALYs) estimate the utility derived from health profiles by taking account of life expectancy and quality of life. In applying QALYs to situations where health varies over time, it is usual to assume that we can add the utilities from constituent health states. This paper investigates the QALY approach to combining health states over time using two tests. The first test rejects additive independence, the central assumption of the QALY model, for individual respondents. The second test is equivocal. The tests are, therefore, unable to conclusively reject the QALY approach to combining health states over time.