Volume 30 - Article 56 | Pages 1561-1570
Is the fraction of people ever born who are currently alive rising or falling?
|Date received:||14 Dec 2013|
|Date published:||16 May 2014|
|Keywords:||exponential, historical demography, people ever born, people ever lived, super-exponential|
|Weblink:||All publications in the ongoing Special Collection 8 "Formal Relationships" can be found at http://www.demographic-research.org/special/8/|
Background: Some journalists and demographers have asked: How many people have ever been born? What is the fraction F(t) of those ever born up to calendar year t who are alive at t? The conditions under which F(t) rises or falls appear never to have been analyzed.
Objective: We determine under what conditions F(t) rises or falls.
Methods: We analyze this question in the model-free context of current vital statistics and demographic estimates and in the context of several demographic models.
Results: At present F(t) is very probably increasing. Stationary, declining, and exponentially growing population models are incapable of increasing F(t), but a doomsday model and a super-exponential model generate both increasing and decreasing F(t).
Conclusions: If the world's human population reaches stationarity or declines, as many people expect within a century, the presently rising fraction of people ever born who are now alive will begin to fall.
Comments: It is curious that nearly all empirical estimates of the number of people ever born assume exponential population growth, which cannot explain increasing F(t).
Joel E. Cohen - Rockefeller University, United States of America
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