Compare methods

	Lexis Diagram	Stable Population Theory
Field	Demography	Demography
Family	Process / pipeline	Regression model
Year of origin	1875	1972
Originator	Wilhelm Lexis	Alfred J. Lotka; Ansley Coale
Type	Geometric bookkeeping device for demographic events on the age, period, and cohort axes	Mathematical demographic model
Seminal source	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
Aliases	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
Related	4	2
Summary	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.