Disability-adjusted life year

Global distribution of DALYs per 100,000 people in 2004.

Infographic explaining the concept of DALY.

Graph showing the weight of disability in DALY calculations.

A disability-adjusted life year (DALY) is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability, or early death. It was developed in the 1990s as a way to compare the overall health and life expectancy of different countries and populations. The DALY metric is used by the World Health Organization (WHO) and other health organizations to assess the burden of disease and to prioritize health interventions.

Definition

The DALY is calculated as the sum of two components:

1. Years of Life Lost (YLL) due to premature mortality in the population.
2. Years Lost due to Disability (YLD) for people living with the health condition or its consequences.

The formula for DALY is:

\[ \text{DALY} = \text{YLL} + \text{YLD} \]

Years of Life Lost (YLL)

YLL is calculated by multiplying the number of deaths at each age by the standard life expectancy at that age. The standard life expectancy is often based on the highest national life expectancy observed globally.

Years Lost due to Disability (YLD)

YLD is calculated by multiplying the number of incident cases by the average duration of the disease and a weight factor that reflects the severity of the disease on a scale from 0 (perfect health) to 1 (death).

Applications

DALYs are used in public health to:

• Compare the burden of different diseases and health conditions.
• Assess the effectiveness of health interventions.
• Allocate resources and prioritize health policies.

Criticism

Some criticisms of the DALY metric include:

• The use of disability weights, which can be subjective and vary between cultures.
• The focus on mortality and disability, which may overlook other important aspects of health such as mental well-being.

Also see

• Quality-adjusted life year
• Global Burden of Disease Study
• Epidemiology
• Public health