Fixed Regime of Mortality and Fertility: The Uses of Stable Theory

Abstract

A stable age distribution exists when age-specific birth and death rates have been constant over a considerable past period. The stable model is an advance in realism over the stationary population of the life table representing the special case of stability in which births are equal to deaths; though the stable model is restricted, the restriction will turn out to be acceptable for a number of purposes. Stable theory tells what age distribution is implied by a given and fixed regime of age-specific rates of birth and death; conversely, it permits in some instances inferring birth and death rates from an observed age distribution. It tells the cost of old-age pensions as a function of the rate of increase in population. For a given life table and rate of increase, average time of promotion in organizations with some degree of seniority can be calculated. These and other applications of stable theory are the subject of the present chapter. Chapter 10 will show how a regime of mortality and fertility implies kinship numbers. Stable theory can be generalized in various directions by modifying the assumption of a fixed regime, as will be seen in Chapter 9.