HOW MANY AMERICANS ARE ALIVE BECAUSE OF 20TH-CENTURY IMPROVEMENTS IN MORTALITY

The article estimates the number of living Americans who owe their exi stence to mortality declines that have occurred in the twentieth centu ry. The estimate is made by projecting the US population from 1900 to 2000 using the mortality rates of 1900 rather than the rates actually observed. A distinction is made between people who would have been bor n and died and those who would never have been born because of a prere productive death to an ancestor. Results indicate that the US populati on would be only one-half its current size if the mortality conditions of 1900 had been maintained: one-quarter of the population would have been born and died, and one-quarter would never have been born. The p roportion alive because of mortality improvements shows little variati on by sex and age, although it is greatest among the very young and th e very old. Mortality reductions below age 15 contributed about two-th irds of the increase in the number of persons alive today.