Concept Architecture
Concept
Theoretically, Years Lived with Disability (YLD) is a measure of non-fatal health loss representing the number of years lived in less than full health due to disease or injury. It forms one of the two components of the Disability-Adjusted Life Year (DALY) framework developed for the Global Burden of Disease study. YLD exists to quantify morbidity by combining the duration of a health condition with the severity of the associated disability.
Mathematically, YLD is calculated by multiplying the prevalence or incidence of a health condition by an appropriate disability weight and, where applicable, the average duration of the condition. The resulting value represents the equivalent number of years of healthy life lost due to disability within a population.
In practice, YLD is estimated using epidemiological data on disease prevalence or incidence, together with disability weights derived from population-based valuation studies. It is applied in burden of disease analyses, priority setting, resource allocation and comparative assessments of population health.
Purpose
Used to quantify the burden of non-fatal disease, estimate morbidity, calculate Disability-Adjusted Life Years, compare the impact of diseases across populations and support public health and health economic decision-making.
Mathematical Formulae
Primary Formula
Prevalence-based formulation:
YLD = P ? DW
where:
- P = prevalence of the health condition
- DW = disability weight
Supporting Formulae
Incidence-based formulation:
YLD = I ? DW ? L
where:
- I = incidence of the health condition
- DW = disability weight
- L = average duration of disability
Related Mathematical Methods
- Disability-Adjusted Life Year (DALY) calculation
- Burden of disease analysis
- Disability weighting
- Epidemiological modelling
- Life table analysis
Example
A chronic disease affects 2,000 individuals in a population. The disability weight is 0.25.
Using the prevalence-based approach:
YLD = 2,000 ? 0.25 = 500
The disease contributes 500 Years Lived with Disability, representing the equivalent of 500 healthy life years lost due to non-fatal illness.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| PRODUCT | =B2*C2 | Calculate YLD using prevalence and disability weight |
| PRODUCT | =B2*C2*D2 | Calculate incidence-based YLD using incidence, disability weight and duration |
| SUM | =SUM(E2:E100) | Aggregate YLD across diseases or population groups |
| SUMPRODUCT | =SUMPRODUCT(B2:B100,C2:C100) | Calculate total prevalence-based YLD across multiple conditions |
VBA (Optional)
Automate the calculation and aggregation of Years Lived with Disability across multiple diseases, age groups and population cohorts.
Sources
- Murray CJL, Lopez AD, editors. The Global Burden of Disease. Harvard School of Public Health.
- Murray CJL, Acharya AK. Understanding DALYs. Journal of Health Economics. 1997.
- World Health Organization. Global Health Estimates: Methods and Data Sources.
- Global Burden of Disease Collaborative Network. Global Burden of Disease Study Methods.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes. Oxford University Press.
Related Concepts (2)
Frequently Asked Questions (6)
What are years lived with disability?
A component of the disability-adjusted life year representing healthy years lost to a non-fatal condition, found by multiplying its prevalence by its disability weight.
Source: Murray 1994
What do years lived with disability represent?
Years lived with disability represent the healthy years of life lost to living in states of less than full health, and they form the non-fatal component of the disability-adjusted life year. Time spent with a condition is weighted by a disability weight between zero and one that reflects the severity of the associated health loss. Summing these weighted years across a population gives the burden attributable to illness and impairment as distinct from the burden of premature death.
Source: Murray 1994
How are years lived with disability calculated?
In the prevalence approach, the number of people living with a condition at a point in time is multiplied by the disability weight for that condition, giving the healthy years lost to it in that period. In the incidence approach, new cases are multiplied by the average duration of the condition and its disability weight. Both convert time spent in impaired health into an equivalent quantity of healthy years lost, so that non-fatal outcomes can be aggregated across conditions.
Source: Murray 1994
What are disability weights in years lived with disability?
Disability weights place health states on a scale from zero, representing full health, to one, representing a state judged equivalent to death, so that time in a state can be converted to healthy years lost. They are derived from surveys in which respondents compare or value health states described by their consequences. The weights allow conditions of differing severity to be combined on a common scale, and the values assigned strongly influence the resulting estimates of non-fatal burden.
Source: Murray 1994
What are the limitations of years lived with disability?
The estimates depend heavily on the disability weights, whose values reflect whose preferences were elicited and how, and these have been revised over time. Prevalence data for many conditions are incomplete, particularly where diagnosis is limited, so the burden of some conditions is uncertain. Applying a single weight to a condition ignores variation in severity between individuals. Comparisons over time can be affected as much by changes in method as by real changes in health.
Source: Murray 1994
How do years lived with disability combine with years of life lost?
The disability-adjusted life year is the sum of years lived with disability and years of life lost, bringing non-fatal and fatal health loss onto one scale. Years lived with disability capture the health lost while living with a condition, and years of life lost capture the health lost through premature death. Adding them gives a single measure of the burden of a disease or risk factor, allowing conditions that mainly kill and those that mainly disable to be compared.
Source: Murray 1994
Trust Record
Verified by Dr Darrin Baines
British health economist
Professional identity: darrinbaines.org
Verification date: 13 Aug 2025
Content version: 1.0.0
Canonical Identity
- Term code
- HE-EE-DALY-007
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