YLL

Years of Life Lost (YLL) is a public health metric that quantifies the burden of premature mortality in a population. It measures the years not lived by individuals who die before a defined standard life expectancy. YLL is often calculated by summing, for all deaths, the difference between a standard life expectancy and the age at death. In many studies, a fixed standard life expectancy at birth is used to enable comparability across populations and over time; for each death at age a, the YLL equals the remaining expected years of life at age a according to the standard life table.

Calculation typically involves determining the number of deaths from a cause and the remaining life expectancy at the age of death, then aggregating these values across all relevant deaths. This yields a single number or a breakdown by age, sex, cause, or region. YLL is widely used in burden of disease assessments and is a core component of the Disability-Adjusted Life Year (DALY), where YLL is combined with Years Lived with Disability (YLD) to reflect total health loss from a condition.

Uses of YLL include comparing the impact of different diseases or injuries, tracking progress in reducing premature mortality, and informing health policy and resource allocation. It emphasizes the loss associated with deaths occurring at younger ages, highlighting conditions that cause early mortality.

Limitations include dependence on the chosen life expectancy standard, which can affect comparisons. YLL does not capture non-fatal health burdens, morbidity, quality of life, or social and economic consequences beyond mortality. Data quality and completeness also influence accuracy.

Example: 1,000 deaths at age 60 with a standard life expectancy of 80 yield 20 YLL per death, totaling 20,000 YLL.