Examples
Worked examples
- Is an instance
A patient with 2 remaining years of life at a health-state utility of 0.5 (moderate impairment) accrues 1.0 QALY (2 years x 0.5). A treatment that instead gives 4 years of life at that same 0.5 utility produces 2.0 QALYs -- an incremental gain of 1.0 QALY versus the first scenario, the numerator used in an incremental cost-effectiveness ratio (ICER).
- Is an instance
Ten years lived at a utility of 0.7 produces 7.0 QALYs; ten years lived at a utility of 0.5 (the comparator) produces 5.0 QALYs. The difference, 2.0 QALYs, is the health gain a technology appraisal committee weighs against the difference in cost between the two options.
Counter-examples
Looks similar, but isn't
- Not an instance
A DALY (disability-adjusted life year) looks similar but runs in the opposite direction: it counts years of healthy life LOST to disease or disability (a burden-of-disease unit used by the WHO and the Global Burden of Disease study), not years of healthy life gained by an intervention. A trial reporting outcomes purely as 'life-years gained' with no quality-of-life adjustment applied is also not reporting QALYs -- that is a simple survival measure; it only becomes a QALY once a utility weight is applied to each life-year.
Editorial commentary
A QALY (quality-adjusted life year) is a health-outcome unit that combines
the length of time a person lives with the quality of health they experience during that
time. One QALY equals one year of life lived in full health; scores range from 1.0 (perfect
health) down to 0 (death), and can go negative for health states judged worse than death.
QALYs are the standard outcome measure in cost-utility analysis, the branch
of economic evaluation that health technology assessment (HTA) bodies — most visibly the
National Institute for Health and Care Excellence (NICE) in the UK — use to compare the
value of very different interventions (a cancer drug, a hip replacement, a talking therapy) on
one common scale.
How a QALY is calculated
A QALY is the product of two inputs: the number of years spent in a health state, and a
utility weight (also called a health-state value) for that state, on the 0-to-1
scale described above. Multiplying years by utility, and summing across every health state a
person passes through, gives the total QALYs accrued. In UK technology appraisals, NICE
recommends deriving that utility weight using the EQ-5D instrument (most
commonly the EQ-5D-5L), a standardised five-dimension health-related quality-of-life
questionnaire scored against a value set derived from a population survey, so that utility
weights are comparable across disease areas rather than specific to one condition.
Why QALYs matter for research administration
QALYs are not just an academic metric — they are the load-bearing unit inside real
reimbursement decisions. A clinical trial or economic-evaluation team preparing a submission
to NICE, the Institute for Clinical and Economic Review (ICER, the US nonprofit — not to
be confused with the incremental cost-effectiveness ratio, also abbreviated ICER, see below),
or an equivalent HTA body needs QALY-based outcomes reported to a recognised, reproducible
methodology, because the appraisal committee’s cost-effectiveness judgement is built directly
on top of them. CASRAI’s CHEERS 2022 checklist
guide covers the current reporting standard for publishing this kind of economic
evaluation, and the NICE technology
appraisal process guide covers how a QALY-based cost-effectiveness estimate is actually
used inside a live appraisal decision.
QALY vs. related measures
A QALY is easy to confuse with two adjacent measures:
- DALY (disability-adjusted life year). A DALY counts years of healthy life
lost to disease or disability — a burden-of-disease unit used mainly in global
health (the WHO and the Global Burden of Disease study report in DALYs). A QALY counts years of
healthy life gained or retained by an intervention — a benefit unit used mainly
in a single health system’s reimbursement decisions. The two run in conceptually opposite
directions even though both blend quantity and quality of life into one number. - Simple life-years gained. Some trials (particularly in oncology and
cardiovascular disease) report outcomes purely as additional life-years, with no quality
adjustment at all. That is not a QALY calculation — it becomes one only once a utility
weight is applied to each life-year lived.
Frequently asked questions
Is a QALY the same as a “quality of life score”?
No. A quality-of-life score (like a raw EQ-5D-5L utility value) is one of the two inputs to a
QALY calculation, not the QALY itself. The QALY is what you get after multiplying that quality
weight by the duration of time spent in that health state.
Who decides the utility weights?
Utility weights come from population-preference studies (patients or the general public
valuing described health states, historically via methods like time trade-off), not from
clinicians or the HTA body itself. NICE publishes recommended value sets and reference-case
methodology for which instrument and value set to use in a submission.
Can a QALY be negative?
Yes. Health states that respondents rate as worse than death produce a negative utility
weight, and therefore a negative QALY contribution for time spent in that state.
Machine-readable encodings
Use in your systems
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