Bongaarts (2006) projected that in the future “longevity improvements will be larger and population aging will be more rapid than many governments of high income countries expect.” To demonstrate this point, he decomposed life expectancy (LE). As defined by him, the conventional life expectancy at any time equals senescent life expectancy (LEs ) minus the longevity-reducing effects of background and juvenile mortality.

LE = LE s - B – J

where

B = LE s - LE j

J = LE j - LE

Thus

LE_j is the life expectancy without juvenile mortality. It equals the average age of death for a newborn if there is no chance of dying before 25 years. In other words, it is LE at age 25 plus 25. LE_s is the life expectancy if some causes of death, such as cardiovascular disease and cancer, the risk of which increases with age, are removed. Background mortality, by causes such as accidents, violence, and some infectious diseases, is independent of age. Bongaarts studied changes in LE, LE_j , LE_s , B and J for 16 high income countries with records from 1850 to 2000, separately for males and females. The background mortality was estimated from the observed data on force of mortality, using the model