Quality-adjusted life year

The quality-adjusted life year or 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 for money of medical interventions. One QALY equates to one year in perfect health. If an individual's health is below this maximum, QALYs are accrued at a rate of less than 1 per year. To be dead is associated with 0 QALYs. QALYs can be used to inform personal decisions, to evaluate programs, and to set priorities for future programs. The quality-adjusted life year or 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 for money of medical interventions. One QALY equates to one year in perfect health. If an individual's health is below this maximum, QALYs are accrued at a rate of less than 1 per year. To be dead is associated with 0 QALYs. QALYs can be used to inform personal decisions, to evaluate programs, and to set priorities for future programs. The QALY is a measure of the value of health outcomes. It assumes that health is a function of length of life and quality of life, and combines these values into a single index number. To determine QALYs, one multiplies the utility value associated with a given state of health by the years lived in that state. A year of life lived in perfect health is worth 1 QALY (1 year of life × 1 Utility value). A year of life lived in a state of less than perfect health is worth less than 1 QALY; for example, 1 year of life lived in a situation with utility 0.5 (e.g. bedridden, 1 year × 0.5 Utility) is assigned 0.5 QALYs. Similarly, half a year lived in perfect health is equivalent to 0.5 QALYs (0.5 years × 1 Utility). Death is assigned a value of 0 QALYs, and in some circumstances it is possible to accrue negative QALYs to reflect health states deemed 'worse than dead.' The 'weight' (utility) values between 0 and 1 are usually determined by methods such as those proposed in the Journal of Health Economics: Another way of determining the weight associated with a particular health state is to use standard descriptive systems such as the EuroQol Group's EQ-5D questionnaire, which categorises health states according to five dimensions: mobility, self-care, usual activities (e.g. work, study, homework or leisure activities), pain/discomfort and anxiety/depression. Data on medical costs are often combined with QALYs in cost-utility analysis to estimate the cost-per-QALY associated with a health care intervention. This parameter can be used to develop a cost-effectiveness analysis of any treatment. This incremental cost-effectiveness ratio (ICER) can then be used to allocate healthcare resources, often using a threshold approach. In the United Kingdom, the National Institute for Health and Care Excellence, which advises on the use of health technologies within the National Health Service, has since at least 2013 used '£ per QALY' to evaluate their utility. The concept of the QALY is credited to work by Klarman et al. (1968), Fanshel and Bush (1970), and Torrance et al. (1972) who suggested the idea of length of life adjusted by indices of functionality or health. A 1976 article by Zeckhauser and Shepard contained the first known occurrence in print of the term 'Quality Adjusted Life Years'. QALYs were later promoted through medical technology assessments conducted by the US Congress Office of Technology Assessment. Then, in 1980, Pliskin et al. proposed a justification of the construction of the QALY indicator using the multiattribute utility theory: if a set of conditions pertaining to agent preferences on life years and quality of life are verified, then it is possible to express the agent's preferences about couples (number of life years/health state), by an interval (Neumannian) utility function. This utility function would be equal to the product of an interval utility function on 'life years', and an interval utility function on 'health state'. According to Pliskin et al., the QALY model requires utility independent, risk neutral, and constant proportional tradeoff behaviour. Because of these theoretical assumptions, the meaning and usefulness of the QALY is debated. Perfect health is difficult, if not impossible, to define. Some argue that there are health states worse than being dead, and that therefore there should be negative values possible on the health spectrum (indeed, some health economists have incorporated negative values into calculations). Determining the level of health depends on measures that some argue place disproportionate importance on physical pain or disability over mental health.