Fertility and Mortality Estimation Using Model Stable Age Distributions

Lotkai proved that the age distribution of any population that is subject, for a sufficiently long time, to constant fertility and mortality becomes fixed. He called this end-product of constant demographic conditions a "stable population", characterized both by an unchanging age distribution and by a fixed annual rate of natural increase. The age distribution of a stable population is jointly determined by the mortality schedule (that is, by the life table) to which the population has been subject and by its annual rate of growth. In chapter I, section C, the equation defining the density function determining the age distribution of a stable population was presented. It has the form