Disability-adjusted life years (DALYs)
- Measure
They add the years lost by dying early and the years lived with illness or disability. One DALY is one year of healthy life lost.
What it is
The DALY is the burden-of-disease measure used by WHO. It adds two parts: years of life lost to premature death (YLL) and years lived with disability (YLD), the latter weighted by the severity of the health state. It puts diseases that kill and diseases that disable on the same scale.
Formula and reading
- YLL = number of deaths × reference life expectancy at the age of death.
- YLD = (prevalent) cases × disability weight × years with the condition.
- Disability weights come from studies that value health states; 0.2 means losing a fifth of a healthy year for each year.
- WHO publishes global burden-of-disease estimates with the leading causes of DALYs by country.
Worked example
- A made-up district, one year. Disease A: 20 deaths at age 50, when each person had 30 years of reference life left.
- YLL for A: 20 × 30 = 600 years lost to premature death.
- Also, 500 people live with A for the whole year, with a disability weight of 0.2: YLD = 500 × 0.2 × 1 = 100.
- DALYs for A: 600 + 100 = 700. Deaths contribute 600 / 700 = 86% of the burden (rounded).
- Disease B does not kill, but 2,000 people live with it all year at weight 0.35: DALYs = 2,000 × 0.35 × 1 = 700.
- Reading: A and B weigh the same, 700 years of healthy life lost, although B causes no deaths at all.
Burden and benefit measures
| Measure | What it adds | Typical use |
|---|---|---|
| YPLL | Years lost before a cut-off age | Premature mortality in a community |
| DALY | Years lost to premature death + years lived with disability | Burden of disease and public health priorities |
| QALY | Years of life weighted by quality | Benefit of an intervention in economic evaluation |
Markers
- DALY
- YLL
- YLD
- Burden of disease
How to read it
- Burden-of-disease studies guide which problems national and territorial public health plans prioritise.
- Cost per DALY averted is used in some economic evaluations, especially of public health programmes.
Common pitfalls
- Adding deaths and cases without weighting: YLD needs the disability weight and the duration.
- Confusing DALYs with QALYs: one is lost, the other gained.
- Forgetting that disability weights are social valuations and change between versions of the studies.
Test yourself
Think of the answer, then tap the question to see it.
Which two components make up a DALY?
Years of life lost to premature death (YLL) and years lived with disability (YLD).
Ten people die at an age when they had 40 years of reference life left. How many YLL is that?
10 × 40 = 400 years of life lost to premature death.
What does a disability weight of 0.5 represent?
That one year in that health state equals losing half a year of healthy life.
Why can a disease that does not kill have many DALYs?
Because DALYs also count years lived with disability; if it is common, long or disabling, it adds a large burden.
Connections
Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.
Sources: Global health estimates: Leading causes of DALYs (World Health Organization, 2026); Healthy life expectancy (HALE) (World Health Organization, 2026).
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Representative model, for educational purposes only.