Quality-Adjusted Life Year (QALY)
Also known as: QALY, health utility measure
A QALY measures health benefit as utility weight (0 = death, 1 = perfect health) multiplied by time lived. Developed by Alan Williams in 1985, QALYs enable comparison of disparate health interventions on a common metric. Used globally by health technology assessment bodies—NICE (UK), HAS (France), CADTH (Canada), WHO—to decide which treatments deserve public funding.
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When to use it
When a health intervention (drug, device, procedure, public health program) affects both length and quality of life. QALY analysis is mandatory for health technology appraisal (HTA) submissions in most developed countries. Use when comparing treatments across disease areas (diabetes vs cancer), or when quality-of-life improvements matter as much as mortality reduction. Not appropriate for: interventions with non-health benefits (education, employment); acute single events (one-time surgery outcome); or settings where equity concerns override efficiency (QALY is utilitarian, not egalitarian).
Strengths & limitations
- Integrates mortality and morbidity into one metric, enabling cross-disease comparison and resource allocation at system level.
- Utility weights derived empirically from population preferences (not clinician opinion), anchoring valuation in patient/public values.
- Transparent, auditable methodology: NICE and other HTAs publish detailed QALY models, allowing replication and critique.
- Accepted internationally by regulators and payers, reducing negotiation friction for market access.
- Utility elicitation is time-consuming and subject to response bias; VAS and TTO produce different utility scores for the same health state.
- QALY assumes additive time × utility model; assumes constant utility over time; ignores duration effects (1 year at 0.5 utility ≠ same as 0.5 years at 1.0).
- Does not capture equity: a QALY to a healthy person equals a QALY to a severely disabled person, violating fairness intuitions in some contexts.
- Health utility varies by culture, age, comorbidity; transferring UK EQ-5D tariffs to low-income countries may misrepresent local preferences.
- Disability scholars argue QALY discriminates against people living with chronic conditions (assigns lower baseline utility, reducing calculated benefit of interventions for disabled groups).
Frequently asked
How are utility weights assigned if a health state is not directly measured?
Mapping or extrapolation. If a trial uses disease-specific scales (e.g., EORTC QLQ-C30) but not EQ-5D, researchers use published mapping algorithms to convert disease scores to EQ-5D utilities. Alternatively, they conduct a small utility study in similar patients. Mapping reduces precision; direct measurement preferred.
What is the difference between QALY and DALY?
QALYs measure health gained (0 = death, 1 = perfect health); DALYs measure disease burden (0 = perfect health, 1 = death). QALY = utility × time (positive framing); DALY = YLL (years of life lost to death) + YLD (years lived with disability). NICE uses QALYs; WHO GBD uses DALYs. Inverse relationship: QALY gained ≈ DALY averted.
Why is discounting applied to QALYs in the future?
Time preference: society values immediate health more than delayed health (£1 today > £1 in 10 years). Standard rate in UK/Canada is 3–5% annually. A 1 QALY in year 10 is worth ~0.7 QALYs in net present value at 3% discount rate. Prevents overinvestment in interventions with distant, small benefits.
Is the EQ-5D utility valid for all populations?
No. EQ-5D tariffs vary by country (UK, France, Germany, US tariffs differ). EQ-5D is less sensitive in mild disease states and in pediatric populations. Cultural values, disability prevalence, and healthcare experience affect utility elicitation. When applying EQ-5D to a new population, a local valuation study is ideal; if not feasible, explicit sensitivity analyses comparing tariffs are required.
Can a treatment have negative QALYs (utility worse than death)?
In principle, yes, if a treatment extends life but creates a health state perceived as worse than death (utility < 0). In practice, most instruments cap minimum utility at 0 (equivalent to death) or slightly negative (rare, severe states). Interventions producing net negative QALYs are not recommended.
How is uncertainty in QALYs handled in cost-effectiveness analysis?
Sensitivity analysis: deterministic (vary utility ± 10%, discount rate ± 1%, time horizon ± years one at a time) and probabilistic (Monte Carlo simulation drawing 10,000 samples from distributions of all parameters). Acceptability curve plots probability that intervention is cost-effective across a range of willingness-to-pay thresholds. Scenario analysis tests structural assumptions (e.g., different utility instruments).
Sources
- Kind, P. (1989). The EuroQol instrument: an index of health-related quality of life. In B. Teeling Smith (Ed.), Measuring health: a practical approach. Chichester: Wiley. link ↗
- Weinstein, M. C., & Stason, W. B. (1976). Hypertension: A Policy Perspective. Cambridge, MA: Harvard University Press. link ↗
- Brooks, R. (1996). EuroQol: the current state of play. Health Policy, 37(1), 53-72. DOI: 10.1016/0168-8510(96)00822-6 ↗
How to cite this page
ScholarGate. (2026, June 4). Quality-Adjusted Life Year (QALY). ScholarGate. https://scholargate.app/en/health-economics/quality-adjusted-life-year
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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