This blog is intended to go along with Population: An Introduction to Concepts and Issues, by John R. Weeks, published by Cengage Learning. The latest edition is the 12th (it came out in 2015), but this blog is meant to complement any edition of the book by showing the way in which demographic issues are regularly in the news.

If you are a user of my textbook and would like to suggest a blog post idea, please email me at: john.weeks@sdsu.edu

Wednesday, May 24, 2017

How Many Old People Have Ever Lived?

This is the question answered by a paper just published in Demographic Research by researchers at the Wittgenstein Centre for Demography and Global Human  Capital in Vienna. Here's what prompted them to look at this issue:
A recent [2014] article in the Economist describes how those “age invaders” are about to change the global economy. Besides the old age dependency ratio, in this publication another indicator of aging is mentioned: The ratio 65 or older alive today relative to all humans who have ever reached the age of 65. According to the Economist , Fred Pearce presumed that it is possible that half of all people who have ever been over 65 are alive today. Motivated by these discussions, in our paper we reconsider indicators that estimate the share of people above a specific age alive today in relation to all the humans who have ever reached this specific age. By using formal demography together with historical data on population processes, we show how such indicators can be estimated. Our results indicate that far fewer than half of all people who have ever been over 65 are [were] alive in 2010.
Indeed, their results suggest that "the proportion who have ever been over 65 that are alive today (as of 2010) ranges between 5.5 and 9.5%." You can compare these numbers with my latest estimates (in the 12th edition) of the percentage of all humans ever born who are currently alive:

In fact, our current contribution to history’s total represents only a relatively small fraction of all people who have ever lived. The most analytical of the estimates has been made by Nathan Keyfitz (Keyfitz 1966; Keyfitz and Caswell 2005), and I have used Keyfitz’s formulas to estimate the number of people who have ever lived, assuming conservatively that we started with two people (call them “Adam and Eve” if you’d like) 200,000 years ago. The results of these calculations suggest that a total of 62.6 billion people have been born, of whom the 7.3 billion estimated to be alive in 2015 constitute 11.7 percent. (Weeks, 12th edition, page 34.)
Interestingly enough, I blogged about the Economist's story on aging at the time, but for whatever reason did not pick up on and try to correct the comment that perhaps half of all people ever to reach age 65 were currently alive. Thanks to the folks in Vienna for filling in that gap. 

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