The age composition of populations experiencing no mortality and various kinds of fertility is derived. It is then shown that, if successive mortality schedules can be expressed as the sum of a component that varies with age and a component that varies with time, only the former has any effect on the age structure of the population. One implication is that a population in which mortality varies with time but not with age has the same composition as a population with no mortality at all.

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Coale, Ansley J. 1959. Increases in Expectation of Life and Population Growth. In the Proceedings of the International Union for the Scientific Study of Population, Vienna, 1959.
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Theorie Analytiqus des Association Biologiques. Part II
Hermann and Cie