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I wish Julian Simon were around to read this passage from "The Low-Fertility Trap Hypothesis: Forces that May Lead to Further Postponement and Fewer Births in Europe":
In the past decades, population projections were based on the expectation that after the end of the demographic transition, life expectancy would reach a certain maximum level... The United Nations population projections give the longest series of consistent projections for all countries in the world and serve as a model for a large number of national population projections. Until very recently, they have assumed that there is a maximum life expectancy that no country in the world will surpass. In the 1973 assessment, this maximum life expectancy was assumed to be 72.6 years for men and 77.5 years for women (Bucht 1996). As time passed, many countries came close to or even passed this assumed maximum life expectancy. As a consequence, the UN has been slowly moving the assumed maximum life expectancy upwards. In the 1982 assessment of the UN projections, the maximum age was assumed to be 75 years for men and 82.5 years for women.  Only 20 years after this assumption was made, a large number of countries had again already surpassed the assumed maximum age and the trend in increasing life expectancy shows no sign of levelling off. In fact, the trend in the countries with the world's highest life expectancy at any point in time shows an almost perfectly linear trend for more than a century with no sign of levelling off (Oeppen and Vaupel 2002). As a consequence, in their most recent population projections, the UN has given up the assumption of a maximum life expectancy and assumes continuing improvements, although at a decelerating speed (UN 2004).
I can't remember the last time anything was better than my maximum estimate.  I wonder how the U.N. statisticians felt to see their maxima exceeded twice.  Happy that the world was so wonderful, or depressed that their insight was so poor?


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COMMENTS (6 to date)
Felix writes:

Happy that the world was so wonderful, or depressed that their insight was so poor?

Would that not depend upon whether U.N. statisticians view older, healthier, or more people as assets or as liabilities?

Or, given the answer to that question, would we know the answers to quite a number of other questions?

SydB writes:

"Happy that the world was so wonderful, or depressed that their insight was so poor?"

I believe the UN population folks are looking at the best evidence available at the time. Which is THE ONLY DEFENSIBLE WAY to make a prediction.

They are not in the business of pulling numbers out of the air as do many cornucopians. The numbers produced by the latter are almost useless.

Seems like the UN is doing exactly what they should be doing.

In other words, nothing to see here folks. Keep moving.

Mark Bahner writes:

"In other words, nothing to see here folks. Keep moving."

Nonsense. The UN people should have been assuming that the maximum age would continue its upward trend. There was more evidence to support that the trend would continue upward than there was evidence to support that the trend would stop.

SydB writes:

They're better off using current values. I see no reason the difference between men dying at 72.6 years and 75 years, for example, has any appreciable bearing upon overall population numbers. Even if revised up from there. I think the UN is better off using real data based upon developed nations--e.g. birth rates--than to pull numbers out of a hat.

Dr. T writes:

It's obvious to me that the UN statisticians needed to speak with some good geriatricians. The problem with the statistics was with the underlying assumptions. The UN statisticians assumed there would be no significant medical advances related to longevity. That is equivalent to assuming no significant future advances in agricultural productivity. The UN statisticians were not "doing exactly what they should be doing." They were lazy and used old trend data to project future changes in longevity without considering the effects of modern medicine.

SydB scoffs at a 2.4 year increase in longevity. But, a 3% increase in lifespan has a signficant affect on total population. The number of person-years goes from 494 to 510 billion. That's the equivalent of 213 million births. Since annual births are 154 million, the effect of increased longevity is equivalent to 1.4 years of births.

agnostic writes:

The other thing to keep in mind about a small change in the expected value -- this will have huge consequences in the right tail, such as people living past 90 or 100 nowadays vs. 50 or 100 or 1000 years ago.

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