Stationary population

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Stationary population  (STATIONARY population)


It can be shown that when a closed population (701-4) is subjected to constant age-specific fertility and mortality rates (631-8; 412-1) for a sufficiently long period of time, its annual rate of increase will tend to become constant. This constant rate of increase is called the intrinsic rate of natural increase 1 or true rate of natural increase 1, and a population .which has reached this stage is called a stable population 2. The proportion of persons in different age groups in such a population will be constant, i.e., the population will have a stable age distribution 3 which is independent of the initial age distribution 4 and depends only on the fertility and mortality rates that obtained. Human populations never reach stability in practice, as fertility and mortality rates constantly change, but the computation of a stable population as a model may serve as an index of the growth potential 5 of a set of age-specific fertility and mortality rates. A stable population in which the rate of natural increase is zero is called a stationary population 6, in such a population the numbers in a given age group are equal to the integral of the survivorship function (431-3) of the life table taken between the upper and lower age limits of the group. A logistic population 7 growing in accordance with the logistic law of growth is one in -which the rate of growth decreases as a linear function of the population already alive and which will tend asymptotically to an upper limit.

  • 2. The crude birth and death rates of a stable population, are called the Stable birth rate and the stable death rate respectively.


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