New research has been recently published by a group of demographers at the social science research organisation, NORC, at the University of Chicago. From it we get an insight into the danger of making population projections (or even making current population estimations).
Now, this research is very technical, but in essence it “contradicts a long-held belief that the morality rate of Americans flattens out above age 80.” The research, undertaken by a husband and wife team, the Gavrilovs, and published in the current edition of the North American Actuarial Journal, “is based on highly accurate information about the date of birth and the date of death of more than nine million Americans born between 1875 and 1895.” According to the PR Newswire:
“The key finding is straightforward–the rate of mortality growth with age of the oldest Americans is the same as that for those who are younger. The research reveals that mortality deceleration, the long-held belief that the mortality rate flattens out above age 80, does not take place…
The mortality rate for people between the ages of 30 and 80 follows what is called the Gompertz Law, named for its founder, Benjamin Gompertz, who observed in 1825 that a person’s risk of death in a given year doubles every eight years of age. It is a phenomenon that holds up across nations and over time and is an important part of the foundation of actuarial science.
For approximately 70 years, demographers have believed that above age 80 the Gompertz Law did not hold and that mortality rates flattened out. The work done by the Gavrilovs, a husband-and-wife team, reveals that the Gompertz Law holds at least through age 106, and probably higher, but the researchers say mortality data for those older than 106 is unreliable.”
The research explains why there have been such discrepancies in the past estimations of the number of old people in the US:
“It also explains why there are only half as many people in the U.S. age 100 and above than the Census Bureau predicted there would be as recently as six years ago… Six years ago, the bureau predicted that by 2010 there would be 114,000 people age 100 or older. The actual number turned out to be 53,364. The projection was wrong by a factor of two…Prior estimates of the number of centenarians in the United States were made in less direct ways that were subject to error. They depended, for example, on people self-reporting their age in the U.S. Census, which is less reliable than having actual birth and death data.”
What can one take from all this? First, if you make it to the 100 mark you are even more tenacious and special than we thought you were before (unless you’re lying about your age in census forms – in which case, shame on you). Secondly, predictions about the state of populations can be extremely difficult to make, especially when it comes to the very old. Thus, predictions reported on this blog in the past about “hordes” of old people aged over 100 in the decades ahead may prove to be somewhat wide of the mark. It also seems that the estimates that the US will have between 265,000 and 4.3 million (!) centenarians by the year 2050 will also be on the high side of reality. What this research serves to remind us is that estimations of populations are only estimations. They may in fact be wrong (sometimes wildly wrong). However, censuses, population predictions and extrapolations are what we have to go on when commenting on population and demography. Without even their light (admittedly distorted at times) we would be stumbling in the dark. Having said that, this report should give us cause to hesitate before we plunge headlong into policies that have far-reaching effects but are based upon data that is perhaps unreliable. Not only do we not know where our temerity will land us in the future, we do not even necessarily know exactly what position we are jumping from.