The baby of today has the prospect of a much longer average lifetime than did the baby of two generations ago. The average duration of life and the death rate are two complementary magnitudes. If the death rate could be accurately established for any period, it would be an easy matter to calculate the span of life in a population in which the annual number of deaths equals the annual number of births, and without emigration or immigration. Such equalities exist in few countries, least of all in the United States. It was calculated by Willcox some years ago that the annual death rate in the United States was about 18 per thousand. On this basis the average length of life would be fifty-five years, obviously a rather high estimate for this country, involving errors of assumption which cannot readily be eliminated from the statistical calculations. For this reason it is ordinarily preferable to be satisfied with a statement of the “crude death rate,” or the quotient of the number of deaths in the year divided by the population. Such figures are easier to obtain.
The Falling Death Rate and Lengthening of Life. JAMA. 2016;316(15):1603. doi:10.1001/jama.2015.17106