, Volume 48, Issue 4, pp 1581–1599 | Cite as

On Nonstable and Stable Population Momentum

  • Thomas J. Espenshade
  • Analia S. Olgiati
  • Simon A. Levin


This article decomposes total population momentum into two constituent and multiplicative parts: “nonstable” momentum and “stable” momentum. Nonstable momentum depends on deviations between a population’s current age distribution and its implied stable age distribution. Stable momentum is a function of deviations between a population’s implied stable and stationary age distributions. In general, the factorization of total momentum into the product of nonstable and stable momentum is a very good approximation. The factorization is exact, however, when the current age distribution is stable or when observed fertility is already at replacement. We provide numerical illustrations by calculating nonstable, stable, and total momentum for 176 countries, the world, and its major regions. In short, the article brings together disparate strands of the population momentum literature and shows how the various kinds of momentum fit together into a single unifying framework.


Population momentum Age distribution Decomposition 



An earlier version of this article was presented at the annual meetings of the Population Association of America, Detroit, MI, April 30–May 2, 2009. Partial support for this research came from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (Grant #5R24HD047879). We are grateful to Adrian Banner, Laura Blue, Ronald Brookmeyer, Robert Calderbank, Chang Chung, Erhan Cinlar, Dennis Feehan, David Gabai, Diego Hofman, Igor Klebanov, Edward Nelson, John Palmer, David Potere, Germán Rodríguez, Lily Shen, and Shripad Tuljapurkar for useful comments and discussions. Suggestions from two anonymous reviewers have helped to clarify the exposition and highlight essential features of the argument. We thank Chang Young Chung for preparing the figures and Valerie Fitzpatrick for administrative and technical support.


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Copyright information

© Population Association of America 2011

Authors and Affiliations

  • Thomas J. Espenshade
    • 1
  • Analia S. Olgiati
    • 2
  • Simon A. Levin
    • 3
  1. 1.Department of Sociology and Office of Population Research, 249 Wallace HallPrinceton UniversityPrincetonUSA
  2. 2.Woodrow Wilson School of Public and International Affairs and Office of Population ResearchPrinceton UniversityPrincetonUSA
  3. 3.Department of Ecology and Evolutionary BiologyPrinceton UniversityPrincetonUSA

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