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	Keyfitz Entropy	生命表解析
分野	人口学	人口学
系統	Process / pipeline	Survival analysis
提唱年	1977	1984
提唱者	Nathan Keyfitz	Demographic/actuarial tradition; Chiang
種類	Elasticity of life expectancy to proportional mortality change / lifespan dispersion measure	Age-structured mortality estimator
原典	Keyfitz, N. (1977). Applied Mathematical Demography. John Wiley & Sons, New York. ISBN: 9780471473503	Chiang, C. L. (1984). The Life Table and Its Applications. Robert E. Krieger Publishing. ISBN: 978-0-89874-565-2
別名	Life-Table Entropy, Keyfitz-Leser Entropy, Entropy of the Survival Curve	Mortality Table, Actuarial Table, Survival Table, Yaşam Tablosu
関連	4	3
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.	A life table is a systematic, age-structured summary of the mortality experience of a population. It traces a hypothetical cohort of births — conventionally 100,000 — through successive age intervals, recording how many survive, how many die, and how many person-years are lived at each interval. The method was formalized in its modern probabilistic form by Chiang (1984), synthesizing centuries of actuarial and demographic practice into a rigorous statistical framework applicable to human and biological populations alike.