Concept Architecture
Concept
Theoretically, Health-Adjusted Life Year is a summary measure of population health that combines the quantity of life lived with the quality or health experienced during those years into a single metric. It is founded on health utility theory and health expectancy methods, recognising that years of life differ in value according to the health state in which they are lived. The concept exists to enable comparisons of health outcomes across diseases, interventions and populations by integrating mortality and morbidity into a common measure.
Mathematically, a health-adjusted life year is calculated by weighting time lived by a health-state value that reflects the quality of health during that period. The mathematical framework is additive, with each period of survival multiplied by its corresponding health utility weight before summation across the evaluation horizon. The measure forms the basis for several health outcome metrics, including the Quality-Adjusted Life Year (QALY) and Healthy Year Equivalent (HYE).
In practice, health-adjusted life years are estimated by combining survival data with health-state utility values obtained from preference-based instruments such as the EQ-5D, HUI or SF-6D. Health economists use the measure in cost-utility analysis, burden of disease assessment and population health monitoring. Estimates are commonly generated using clinical trial data, observational studies or decision-analytic models.
Purpose
Used to combine survival and health-related quality of life into a single outcome measure for economic evaluation, health technology assessment, population health measurement and comparison of healthcare interventions.
Mathematical Formulae
Primary Formula
HALY = ????? u? ? ?t
where:
- HALY = health-adjusted life years
- u? = health utility weight during period t
- ?t = duration of the period
- T = total evaluation horizon
Supporting Formulae
For equal annual intervals:
HALY = ????? u?
Continuous form:
HALY = ??? u(t) dt
Related Mathematical Methods
- Health utility measurement
- Area-under-the-curve estimation
- Survival analysis
- Cost-utility analysis
- Decision-analytic modelling
- Discounting of health outcomes
Example
A patient survives four years following treatment. Utility values are estimated as 0.90, 0.85, 0.80 and 0.75 for successive years.
HALY = (0.90 ? 1) + (0.85 ? 1) + (0.80 ? 1) + (0.75 ? 1)
HALY = 3.30
The intervention therefore generates 3.30 health-adjusted life years over the four-year period.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| SUMPRODUCT | =SUMPRODUCT(B2:B5,C2:C5) | Calculate health-adjusted life years by multiplying utility weights by time intervals |
| SUM | =SUM(D2:D5) | Sum interval-specific health-adjusted life years |
| IF | =IF(B2<0,0,B2) | Prevent invalid utility values where appropriate |
| NPV | =NPV(0.035,D2:D20) | Discount future health-adjusted life years for economic evaluation |
VBA (Optional)
Automate calculation of health-adjusted life years for multiple patients or model cohorts using time-varying utility profiles and discount rates.
Sources
- Gold MR, Stevenson D, Fryback DG. HALYs and QALYs and DALYs, Oh My: Similarities and Differences in Summary Measures of Population Health. Annual Review of Public Health. 2002.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes. Oxford University Press.
- Torrance GW. Measurement of Health State Utilities for Economic Appraisal. Journal of Health Economics. 1986.
- Briggs A, Claxton K, Sculpher M. Decision Modelling for Health Economic Evaluation. Oxford University Press.
- NICE. Health Technology Evaluation Manual.
Related Concepts (2)
Frequently Asked Questions (7)
What is a health adjusted life year?
A general term for outcome measures, including the QALY and DALY, combining length of life with a weighting for quality or disability into one unit.
Source: Murray 1994
What is a health-adjusted life year?
A health-adjusted life year, or HALY, is a general term for outcome measures that combine length of life with a weighting for quality or disability into a single unit, including the quality-adjusted life year and the disability-adjusted life year. Such measures express health in terms of both how long and how well people live, allowing survival and health status to be captured together. The HALY is the umbrella concept under which these summary measures of population health fall.
Source: Murray 1994
What summary health measure is a health-adjusted life year?
A health-adjusted life year is a summary measure that combines the length of life with its quality into a single figure. It weights time lived by a factor reflecting health-related quality of life, so that a year in poor health counts as less than a year in full health. The family includes the quality-adjusted life year and the disability-adjusted life year, which apply the weighting in different ways. Such measures allow gains in survival and gains in quality to be expressed on one common scale. This supports comparison across very different treatments.
Source: Gold et al. 2002
What measures does the health-adjusted life year encompass?
The health-adjusted life year encompasses summary measures that weight time by health, chiefly the quality-adjusted life year, which weights years by health-related quality of life and counts health gained, and the disability-adjusted life year, which weights years by disability and counts health lost. Both combine length of life with a health weighting into one unit, though they differ in whether they measure health gained or lost and in how the weights are derived. The HALY names the family they belong to.
Source: Murray 1994
Why are health-adjusted life years useful?
Health-adjusted life years are useful because they combine length and quality of life into a single measure, allowing interventions and conditions to be compared on a common scale that reflects both survival and health status. This supports comparison across diseases and across treatments that affect life in different ways, and it underlies cost-effectiveness analysis and the measurement of population health. By expressing health in one unit, HALYs make it possible to weigh gains in longevity against gains in quality of life consistently.
Source: Murray 1994
How do the QALY and DALY differ as health-adjusted life years?
The QALY and DALY are both health-adjusted life years but differ in orientation and construction. The QALY measures health gained, weighting years by quality of life on a scale where full health counts as one, and is used chiefly in cost-effectiveness analysis. The DALY measures health lost, weighting years by disability and adding years lost to premature death, and is used chiefly to measure disease burden. They share the idea of weighting time by health but express it from opposite directions.
Source: Murray 1994
What are the limitations of health-adjusted life years?
Health-adjusted life years have limitations common to combining length and quality into one figure. The weights for quality or disability require value judgements about how to rate health states, which are contested and vary by method and whose values are used. Combining longevity and quality into a single number can obscure the different components of a change. The measures may also embed assumptions, such as that a QALY is of equal value to whoever receives it, that raise equity concerns.
Source: Murray 1994
Trust Record
Verified by Dr Darrin Baines
British health economist
Professional identity: darrinbaines.org
Verification date: 16 Sep 2025
Content version: 1.0.0
Canonical Identity
- Term code
- HE-EE-QALY-003
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