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	Lexis Diagram	安定人口理論
分野	人口学	人口学
系統	Process / pipeline	Regression model
提唱年	1875	1972
提唱者	Wilhelm Lexis	Alfred J. Lotka; Ansley Coale
種類	Geometric bookkeeping device for demographic events on the age, period, and cohort axes	Mathematical demographic model
原典	Preston, S. H., Heuveline, P., & Guillot, M. (2001). Demography: Measuring and Modeling Population Processes. Blackwell. ISBN: 9781557864512	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	Lexis surface, Age-period-cohort diagram, Lexis grid, Lexis Diyagramı	Lotka-Coale Stable Population Model, Stable Age Distribution Theory, Stationary Population Theory, Kararlı Nüfus Teorisi
関連	4	2
概要	The Lexis diagram is a geometric bookkeeping device that places every demographic event in a two-dimensional grid of age against calendar time, so that each person's life traces a diagonal line and each cohort fans out as a band of parallel lifelines. Named after the German statistician Wilhelm Lexis, it is the foundational drawing of formal demography: it makes the otherwise confusing relationship between age, period, and birth cohort visible, and it tells the analyst exactly which deaths, births, and person-years belong together when a rate is computed.	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.