Adding extrinsic goals to the quality-adjusted life year model

Methods for evaluating health quality are central to medical decision analyses. The most important such method is the quality-adjusted life year (QALY), in which a patient's length of life is given weight proportional to his/her quality of health. QALYs have become ubiquitous in medical cost-effectiveness as a measure of preference for health outcomes. However, numerous studies have demonstrated that the correlation between measured QALYs and a patient's current health is at best modest. Moreover, it is known that individuals may trade lifetime for improved health quality when remaining lifetime is long, but not when it is short; and those with poor health quality may prefer to survive only until important life milestones and no longer. These behaviors are inconsistent with the QALY model. To address these concerns, we examine methods for including life goals in health preference models. The QALY model already captures ongoing goals such as minimizing chronic pain or maintaining physical mobility, goals whose achievement has impact proportional to length of life. However, other goals, termed extrinsic goals, such as completing an important project or seeing a child graduate from college, are qualitatively different – their achievement has impact that is independent of length of life, and therefore cannot be captured using QALYs. In this paper, we present a generalization of the QALY model that incorporates both ongoing goals and extrinsic goals. The new model allows the plausible behaviors mentioned above but forbidden by the QALY model.