Quality-adjusted life year (QALY)

The quality-adjusted life year (QALY) is a summary outcome measure used to quantify the effectiveness of a particular intervention. Since the benefits of different interventions are multi-dimensional, QALYs combine the impact of gains in quality of life and quantity of life (i.e. life expectancy) associated with an intervention. In this case, the incremental (i.e. differences between two or more alternatives) QALYs compared with the incremental costs provide the measure of economic value. If a wide range of aspects (domains) of quality of life is included in the quality component, the resulting QALYs should be comparable across disease areas, which is valuable when considering broad-based resource allocation decision making. More specifically, QALYs are based on utilities, which are valuations of health-related quality of life measured on a scale where full health is valued as 1 and death as 0. These valuations are then multiplied by the duration of time (in years) that a subject spends in a health state with that particular utility score, and aggregate QALYs are then summed over the subject’s projected lifetime (or other time period corresponding to the time horizon of the analysis). For example, if someone experiences a health state with a utility of 0.8 for 10 years and then a health state with a utility of 0.5 for 5 years (and then dies), their aggregate QALYs will be (0.8×10) + (0.5×5) = 10.5 QALYs. QALYs are recommended by the National Institute for Health and Care Excellence (NICE) as its preferred measure of health outcome for use in technology appraisals.