One DALY can be thought of as one lost year of “healthy” life. The sum of these DALYs across the population, or the burden of disease, can be thought of as a measurement of the gap between current health status and an ideal health situation where the entire population lives to an advanced age, free of disease and disability.
DALYs for a disease or health condition are calculated as the sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for people living with the health condition or its consequences:
DALY = YLL + YLD
The YLL basically correspond to the number of deaths multiplied by the standard life expectancy at the age at which death occurs. The basic formula for YLL (without yet including other social preferences discussed below), is the following for a given cause, age and sex:
YLL = N x L
N = number of deaths
L = standard life expectancy at age of death in years
Source: World Health Organization (2018) Health statistics and information systems. Metrics: Disability-Adjusted Life Year (DALY). Quantifying the Burden of Disease from mortality and morbidity. http://www.who.int/healthinfo/global_burden_disease/metrics_daly/en/
Example of the term in use:
The proportion of total DALYs borne by children under 15 years old globally declined from 47% in 2000 to 32% in 2016, reflecting the massive reduction in deaths among children under 5 years old during this period. Almost all (87%) of DALYs borne by children under 15 years old, however, were caused by premature death, the remaining 13% were caused by ill health and disability.
World Health Organization (2018) Global Health Observatory (GHO) data. Disability-adjusted life years (DALYs). https://www.who.int/gho/mortality_burden_disease/daly_rates/text/en/