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	Demographic Balancing Equation	Population Pyramid Analysis
分野	人口学	人口学
系統	Process / pipeline	Process / pipeline
提唱年	1976	1874
提唱者	Classical demographic accounting identity	Francis A. Walker (early age-sex diagrams); standard demographic practice
種類	Population accounting identity for change over a period	Graphical and tabular analysis of population age-sex structure
原典	Preston, S. H., Heuveline, P., & Guillot, M. (2001). Demography: Measuring and Modeling Population Processes. Blackwell. ISBN: 9781557864512	Preston, S. H., Heuveline, P., & Guillot, M. (2001). Demography: Measuring and Modeling Population Processes. Blackwell. ISBN: 9781557864512
別名	Balancing Equation of Population Change, Population Accounting Equation, Components of Population Change Identity	Age-sex pyramid, Population age structure diagram, Age structure analysis, Nüfus Piramidi Analizi
関連	4	4
概要	The demographic balancing equation is the fundamental accounting identity of population change: a population at the end of a period equals its size at the start, plus births, minus deaths, plus in-migrants, minus out-migrants. It is the bookkeeping rule that ties together all the components of population dynamics and guarantees internal consistency in population estimates and projections. Because it is an exact identity, it also serves as a powerful estimation tool — any single unknown component, most often net migration, can be recovered as the residual once the others are known.	Population pyramid analysis is the description and interpretation of a population's age-sex structure through a back-to-back horizontal bar chart, with males on one side, females on the other, and age groups stacked from youngest at the bottom to oldest at the top. The shape of the pyramid encodes a population's fertility, mortality, and migration history and is the demographer's first diagnostic of whether a population is young and growing, ageing, or contracting.