手法を比較

	Pollard Decomposition	Lifespan Inequality
分野	人口学	人口学
系統	Process / pipeline	Process / pipeline
提唱年	1982	2003
提唱者	John H. Pollard	Lifespan-variation literature; life disparity formalized by Vaupel & Canudas-Romo
種類	Age-specific decomposition of a difference in life expectancy	Measures of variability in the age-at-death distribution
原典	Pollard, J. H. (1982). The expectation of life and its relationship to mortality. Journal of the Institute of Actuaries, 109(2), 225–240.	Vaupel, J. W., & Canudas-Romo, V. (2003). Decomposing change in life expectancy: A bouquet of formulas in honor of Nathan Keyfitz's 90th birthday. Demography, 40(2), 201–216.
別名	Pollard's Method, Pollard Life Expectancy Decomposition, Continuous Age Decomposition of Life Expectancy	Lifespan Variation, Life Disparity, Variation in Age at Death
関連	4	4
概要	Pollard's decomposition breaks a difference in life expectancy between two populations into additive contributions from each age, showing exactly how much of the gap is due to mortality differences at infancy, in midlife, or in old age. John Pollard derived a continuous-age formula expressing the life-expectancy difference as an integral of the age-specific mortality-rate difference weighted by life-table functions. Because the contributions sum exactly to the total gap and can be further split by cause of death, the method is a standard tool for explaining why one population outlives another.	Lifespan inequality measures how unequally length of life is distributed within a population — the spread of the life-table ages at death, not just their average. Two populations can share the same life expectancy yet differ sharply in how predictable death is: in one nearly everyone reaches old age, in the other deaths are scattered across all ages. A family of measures — life disparity (e†), the standard deviation of age at death, the life-table Gini coefficient, and Keyfitz entropy — quantifies this dispersion, complementing life expectancy with a measure of how fairly survival is shared.