A method used to measure the benefit of medical intervention. Each additional year of life attributed to the medical intervention is given a value reflecting the quality of life in that year. A value of 1 is given to a year lived in perfect health and a lower value, down to a minimum of 0, is given to any years with illness. Hence, a year lived with mild discomfort may be rated 0.75 but a year with serious illness rated 0.25. The benefit of medical intervention is measured by the QALYs it generates which are defined as the sum of the additional years of life with each year weighted by its value. In a cost–benefit analysis the benefit of treatment is equal to the number of QALYs multiplied by the financial valuation of a year of life (the UK National Institute for Health and Care Excellence uses a value of approximately £30 000). The resulting benefit can be compared to the cost of the treatment to judge whether treatment is economically justified.