Years of potential life lost
) or potential years of life lost
), is an estimation of the average years a person would have lived if he or she had not died prematurely.
It is, therefore, a measure of premature mortality. As a method, it is an alternative to death rates that gives more weight to deaths that occur among younger people.
To calculate the years of potential life lost, the analyst has to set an upper reference age. The reference age should correspond roughly to the life expectancy of the population under study. In the developed world, this is commonly set at age 75, but it is essentially arbitrary. Thus, PYLL should be written with respect to the reference age used in the calculation: e.g., PYLL
PYLLs can be calculated using individual level data or using age grouped data
[ http://www.apheo.ca/index.php?pid=190 Association of Public Health Epidemiologists in Ontario ]
Briefly, for the individual method, each person's PYLL is calculated by subtracting the person's age at death from the reference age. If a person is older than the reference age when he or she dies, that person's PYLL is set to zero (i.e., there are no "negative" PYLLs). In effect, only those who die before age 75 are included in the calculation. Some examples:
1. Reference age = 75; Age at death = 60; PYLL
= 75 - 60 = 152. Reference age = 75; Age at death = 6 months; PYLL
= 75 - 0.5 = 74.53. Reference age = 75; Age at death = 75; PYLL
= 75 - 75 = 04. Reference age = 75; Age at death = 80; PYLL
= 0 (age at death greater than reference age)