# Years of Life Lost

Potential years of life lost (YLL) provide a summary measure of premature mortality. Potential years of life lost may be defined as the years of potential life lost due to premature deaths.

Years of life lost (YLL) take into account the age at which deaths occur, giving greater weight to deaths at a younger age and lower weight to deaths at older age. The indicator measures the YLL due to a cause as a proportion of the total YLL lost in the population due to premature mortality.

YLL is used in public health planning to compare the relative importance of different causes of premature deaths within a given population, to set priorities for prevention, and to compare the premature mortality experience between populations.

Calculating the number of years of life lost

The number of YLL is calculated by summing the number of deaths at each age between 1-74 years, multiplied by the number of years of life remaining up to the age of 75 years.1

i = age

ai = no. years of life remaining to age 75 when death occurs between ages i and i+1
di = no. observed deaths in the population under investigation between aged i and i+1

Assuming a uniform distribution of deaths within age groups, ai = 75 - (i + 0.5) and therefore:

Crude years of life lost rate

The crude YLL is the number of years of life lost divided by the resident population aged

N = number of population

References

1. Compendium of Clinical and Health Indicators User Guide Annex 3. National Centre for Health Outcomes Development. Available at: http://www.nchod.nhs.uk/