Quality adjusted life year

One year in full health counts as one quality adjusted life year. A year lived in a state judged to be half as good counts as a half. The point of the construction is to make two very different treatments comparable: a drug that extends life and a device that improves mobility both produce a number in the same unit.

It exists because a health system with a fixed budget has to choose. Funding one treatment means not funding another, so the question is not whether a treatment helps but whether it helps more per unit of spend than what it displaces.

The measure is contested, and a candidate who says so sounds better informed than one who recites it. Quality weights come from surveys of stated preferences, they compress a complicated experience into one number, and critics argue the method systematically undervalues treatments for conditions affecting older or already disabled populations. Assessment bodies apply modifiers for end of life and rare disease partly in response.

For valuation purposes what matters is that this is the denominator of the ratio the funding decision turns on. A treatment that improves a surrogate marker without moving survival or quality of life will struggle in this framework however good the clinical story sounds.