a measure of a person’s cumulative cigarette consumption over a long period of time. It is expressed as the number of packs (assuming 20 cigarettes in a pack) smoked per day multiplied by the number of years of smoking:
For example, a patient who has smoked 15 cigarettes a day for 40 years has a (15/20) × 40 = 30 pack-year smoking history.
(YLL, years of potential life lost, YPLL, potential years of life lost, PYLL) a measure of premature mortality that calculates the number of additional years a person could have expected to live, on average, had they not died prematurely. A reference age intended to represent the total number of years a person can expect to live, on average, is required for the calculation: this is often given in square brackets after YLL. Negative values for YLL are not used: if somebody survives longer than the reference age, their YLL is calculated as 0. YLLs for different diseases can be compared across populations to give an indication of which diseases carry the greatest burden of premature mortality.... years of life lost
Health Encyclopedia