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	Population Momentum	安定人口理論
分野	人口学	人口学
系統	Process / pipeline	Regression model
提唱年	1971	1972
提唱者	Nathan Keyfitz	Alfred J. Lotka; Ansley Coale
種類	Measure of latent growth from age structure after fertility reaches replacement	Mathematical demographic model
原典	Keyfitz, N. (1971). On the momentum of population growth. Demography, 8(1), 71–80.	Coale, A. J. (1972). The Growth and Structure of Human Populations: A Mathematical Investigation. Princeton University Press. ISBN: 978-0-691-09357-4
別名	Demographic Momentum, Momentum of Population Growth, Keyfitz Momentum	Lotka-Coale Stable Population Model, Stable Age Distribution Theory, Stationary Population Theory, Kararlı Nüfus Teorisi
関連	3	2
概要	Population momentum is the tendency of a growing population to keep growing for decades even after fertility falls to the replacement level, simply because its age structure is heavily weighted toward young people who have yet to reach childbearing age. Introduced by Nathan Keyfitz in 1971, the momentum factor measures how much larger (or smaller) a population will ultimately become if fertility instantly drops to exact replacement. It explains why ending rapid population growth is not immediate: the built-in youthfulness of a fast-growing population carries growth forward long after birth rates stabilize.	Stable Population Theory is a mathematical framework in demography that describes the age structure and growth dynamics of a closed population subject to constant age-specific fertility and mortality schedules over a long period. Foundational work by Alfred J. Lotka established the core integral equation in the early twentieth century, and Ansley Coale's 1972 mathematical synthesis became the definitive theoretical reference, showing that any population exposed to invariant vital rates will converge to a unique stable age distribution growing at a fixed intrinsic rate of natural increase.