Quality-adjusted life year
The quality-adjusted life year (QALY) is a generic measure of disease burden, including both the quality and the quantity of life lived. It is used in economic evaluation to assess the value of medical interventions. One QALY equates to one year in perfect health. QALY scores range from 1 (perfect health) to 0 (dead). QALYs can be used to inform health insurance coverage determinations, treatment decisions, to evaluate programs, and to set priorities for future programs. Critics argue that the QALY oversimplifies how actual patients would assess risks and outcomes, and that its use may restrict patients with disabilities from accessing treatment. Proponents of the measure acknowledge that the QALY has some shortcomings, but that its ability to quantify tradeoffs and opportunity costs from the patient and societal perspective make it a critical tool for equitably allocating resources. The QALY is a measure of the value of health outcomes to the people who experience them. It combines two different benefits of treatment—length of life and quality of life—into a single number that can be compared across different types of treatments. Calculating a QALY requires two inputs. One is the utility value (or utility weight) associated with a given state of health by the years lived in that state. The underlying measure of utility is derived from clinical trials and studies that measure how people feel in these specific states of health. The way they feel in a state of perfect health equates to a value of 1 (or 100%). Death is assigned a utility of 0 (or 0%), and in some circumstances it is possible to accrue negative QALYs to reflect health states deemed "worse than dead." The value people perceive in less than perfect states of health are expressed as a fraction between 0 and 1. The second input is the amount of time people live in various states of health. This information usually comes from clinical trials. To calculate the QALY, the two measures are multiplied. For example, one year lived in perfect health equates to 1 QALY.
