[Dictionary] QALY (Quality-Adjusted Life Year)

A QALY (quality-adjusted life year) is a health-outcome unit equal to one year of life lived in full health (utility = 1.0), calculated by multiplying the number of years spent in a given health state by a utility weight for that state (0 = death, 1.0 = full health, with negative values possible for states considered worse than death) and summing across every health state a person passes through. Health technology assessment bodies, most prominently NICE in the UK, use QALYs as the common outcome unit in cost-utility analysis so that interventions across unrelated disease areas can be compared for cost-effectiveness on a single scale.