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	Keyfitz Entropy	安定人口理論
分野	人口学	人口学
系統	Process / pipeline	Regression model
提唱年	1977	1972
提唱者	Nathan Keyfitz	Alfred J. Lotka; Ansley Coale
種類	Elasticity of life expectancy to proportional mortality change / lifespan dispersion measure	Mathematical demographic model
原典	Keyfitz, N. (1977). Applied Mathematical Demography. John Wiley & Sons, New York. ISBN: 9780471473503	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	Life-Table Entropy, Keyfitz-Leser Entropy, Entropy of the Survival Curve	Lotka-Coale Stable Population Model, Stable Age Distribution Theory, Stationary Population Theory, Kararlı Nüfus Teorisi
関連	4	2
概要	Keyfitz's entropy, usually written H, is a dimensionless summary of a life table that measures how sensitive life expectancy is to a proportional change in mortality, and equivalently how unequal the distribution of ages at death is. Introduced by Nathan Keyfitz, it is the elasticity of life expectancy at birth with respect to the force of mortality: an H near one means deaths are spread across all ages so that reducing mortality everywhere lengthens life proportionally, while an H near zero means deaths are concentrated near the maximum lifespan so further mortality reductions yield little gain. It bridges the demography of survival and the broader study of lifespan inequality.	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.