Calculation
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.
PYLL can be calculated using individual level data or using age grouped data.
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 the reference age are included in the calculation. Some examples:
- Reference age = 75; Age at death = 60; PYLL = 75 - 60 = 15
- Reference age = 75; Age at death = 6 months; PYLL = 75 - 0.5 = 74.5
- Reference age = 75; Age at death = 80; PYLL = 0 (age at death greater than reference age)
To calculate the PYLL for a particular population in a particular year, the analyst sums the individual PYLLs for all individuals in that population who died in that year. This can be done for all-cause mortality or for cause-specific mortality.
Read more about this topic: Years Of Potential Life Lost
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