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	Age-Period-Cohort Model	Lexis Diagram
分野	人口学	人口学
系統	Regression model	Process / pipeline
提唱年	1983	1875
提唱者	Theodore R. Holford (modern estimable-function formulation)	Wilhelm Lexis
種類	Regression decomposition of rates into age, period and cohort effects	Geometric bookkeeping device for demographic events on the age, period, and cohort axes
原典	Holford, T. R. (1983). The estimation of age, period and cohort effects for vital rates. Biometrics, 39(2), 311–324.	Preston, S. H., Heuveline, P., & Guillot, M. (2001). Demography: Measuring and Modeling Population Processes. Blackwell. ISBN: 9781557864512
別名	APC Model, Age-Period-Cohort Analysis, Holford APC Model	Lexis surface, Age-period-cohort diagram, Lexis grid, Lexis Diyagramı
関連	4	4
概要	The age-period-cohort (APC) model decomposes variation in a vital rate — mortality, incidence, fertility — into three temporal dimensions: the age of individuals, the calendar period of observation, and the birth cohort to which they belong. It is the standard framework for asking whether a trend reflects how risk changes with age, contemporaneous period influences affecting all ages at once, or generational effects carried by successive cohorts. Its defining technical challenge is that cohort equals period minus age, an exact linear dependence that makes the three sets of linear effects unidentifiable without further assumptions; Holford's 1983 formulation clarified exactly which quantities can and cannot be estimated.	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.