A QALY is a measuring stick that health people in Britain use when they ask, “How much extra good life does this treatment really give?” The letters stand for Quality-Adjusted Life Year. One QALY is like one whole year of life in very good health. Two extra years that feel only half as good — because of pain, or because you cannot walk far — count as about one QALY, not two. The National Health Service looks at QALYs when it decides whether to pay for a new medicine or operation: not only “Will this keep someone alive?” but “How many extra decent years, and at what cost?” You will meet the word in news about hospitals, new drugs, and government money, not in ordinary chat. It is a useful tool, though actually it is a blunt one. Putting a number on “how good a life feels” is never as tidy as the maths looks, and people argue about whose life the number fits.

品質調整生命年（醫療經濟用語；台灣學界用「品質」。中國大陸較常寫「質量調整生命年」。論文與新聞裡常直接保留 QALY。）