Content of review 1, reviewed on October 06, 2016

Comments about Vijg Letter and Olshansky commentary in Nature 5 October 2016, JWV

This publication is another travesty in a century-long saga of asserted looming limits to average and maximum human lifespan. It is disheartening how many times the same mistake can be made in science and published in respectable journals.

A century ago it was believed that average lifespan—life expectancy—would never exceed 65. As evidence to the contrary poured in, the limit was raised and raised again. Olshansky pegged it at 85. Japanese women today, however, can expect to live more than 87 years.

A century ago the maximum span of life was believed to be about 105. Again this limit was increased as people exceeded it. Vijg and Olshansky set it at 115 even though the current record holder, Jeanne Calment, lived 122.45 years: she is dismissed as an “outlier”.

In this sorry saga, those convinced that there are looming limits did not apply demography and statistics to test hypotheses about lifespan limits—instead they exploited rhetoric, deficient methods and pretty graphics to attempt to prove their gut feelings. The publications are essentially propaganda, not scholarly research.

Vijg’s travesty and Olshansky’s commentary on it in the same issue of Nature are further dismal examples. The material was published and is getting publicity because it seems plausible to many people that average and maximum lifespans cannot increase much more. The main evidence is summarized in colorful graphs that are problematic.

  • It is claimed that life expectancy is plateauing, approaching a looming limit, but the Figures in Vijg, including Fig. 1a for France and subsequent Figures for Japan, Italy and other large countries with high life expectancies, do not support this. They show a continuing rise in life expectancy albeit, in some cases, at a somewhat slower rate than in some earlier periods. There is no evidence that the slower rate will become an even slower rate and then zero.
  • The age at which the most rapid progress is being made in increasing survival is shown to be high—above 100 in recent years—and rising to higher and higher ages. It is claimed that this age plateaued after 1980 but again this is not supported by the graphs. The most important country for the analysis is Japan, a country with a large population and the world’s life expectancy leader. In Japan there is no plateau. Nor is there one for France and Italy, two other countries with large populations and high life expectancies, although there is some deceleration in the rate of increase. Again, there is no evidence that there will be further deceleration leading in the near future to a plateau.
  • Data on the maximum recorded age at death are simplistically and without any statistical justification fit by two lines—a rising line and after 1995 a declining line. More powerful methods, including methods from Extreme Value Theory, should have been used to test whether the data imply a decline in maximum lifespan.

Like analogous, disproven publications over the past 100 years, Vijg et al. and Olshansky add nothing to scientific knowledge about how long we will live. The publications are advocates’ arguments based on selective use of data, with one-sided conclusions not supported by the data.

Source

    © 2016 the Reviewer (CC BY 4.0).

Comments   (Guidelines)

Brandon Milholland

12:35 a.m., 9 Oct 16 (UTC) | Link

We respectfully disagree with Dr. Vaupel in his criticisms on our paper "Evidence for a limit to human life span", Dong et al., Nature 2016.

Our paper is entitled "Evidence for a limit to human lifespan"--not life expectancy. This distinction is important. We agree with Dr. Vaupel that life expectancy will likely continue to increase for the foreseeable future. However, maximum lifespan appeared to have reached its limit. Of course, life expectancy must be lower than maximum lifespan, so it too will reach its limit, but at its current rate of increase of around 0.2 years per year, it will be over a century before it reaches that limit in most countries, even longer if it decelerates as it approaches its ceiling.

How about the main claim of our article, the proposed limit to human lifespan? First, it should be evaluated on its own merits. Previous predictions may have been wrong, but that does not mean ours automatically is also wrong. As for Jeanne Calment, she is not dismissed as an outlier, but was included in our analyses. Her age at death of 122 exceeds our limit of 115, but that figure is not meant as a hard limit but rather the likely value of the world MRAD (maximum reported age at death) in any given year. The MRAD might be higher in some years, as it happened to be in 1997, but higher values are improbable and likely to be followed by a regression to the mean of 115 (hence the downward trend since Calment's death). Calment's exceptional longevity did prompt us to attempt to calculate the ultimate limit to human lifespan: we calculated that the MRAD would exceed 125 only once every 10,000 years. Since this time frame is longer than all of human history to date, we consider our estimate of the outer reaches of human lifespan to be a fairly liberal one.

Below we respond to each of Dr. Vaupel's points:

  • Figure 1a and the corresponding graphs in Extended Data Figure 1 do show increasing life expectancies, but, as we have explained, this does not undermine the thesis of the article.

  • As for the age at which the most rapid progress is being made, i.e. our Figure 1d, the plateau seems fairly obvious to us. In France, looking at the years prior to 1980, the age with the greatest increase in survival goes up every few years, but since then it has only gone up rarely. In females it went up to 103 in 2004, went back down to 102 the next year, and then up to 103 in 2007, so it looks like it is not really going up but perhaps fluctuating between 102 and 103; regardless, there hasn't been an increase for a decade (the most recent data available is for 2014). As for males, it increased to 101 in 2008, but before that it has been at 100 since 1981. This represents an increase of one in an interval of over 30 years; contrast that with the 30-year interval 1950-1980 where it increased 12 years, from 87 to 99. It is possible that the ages with the highest gain might creep up another year or two, but their slow rate of increase over the past few decades seems to indicate that they have either reached or will soon reach their limit. There is a similar situation in Italy, where the age with the greatest gain has remained stagnant since 2004 (in females) and 2002 (in males); and in Japan, where the corresponding years are 2004 and 1998.

  • If the MRAD were increasing continuously without limit, then splitting the data into two parts should result in linear regressions with positive slopes in both parts. Instead, we find that the first half has a positive slope, while the second half has a negative slope. The latter is not significant, so we conclude that the MRAD is essentially flat and does not vary in a manner correlated with time after the 1990s. As an additional validation, we re-analzyed the data from Figure 2a using a segmented regression (R package “segmented", reference “https://www.researchgate.net/publication/234092680_Segmented_An_R_Package_to_Fit_Regression_Models_With_Broken-Line_Relationships”). The package automatically detect breakpoints. In the first model, segmented regression, the MRAD shows a linear increase between 1968 and 1998 (one year after Calment’s death) of 0.20 per year; then it decreases linearly between 1999 and 2006 by 0.69 per year. This model has an adjusted R-squared of 0.41 and an AIC of 140.7. In the second model, linear regression of the entire dataset, the MRAD shows a linear increase of 0.12 per year, with an adjusted R-squared of 0.27 and an AIC 146.2. With a higher R-squared and a lower AIC, the first model, segmented regression, is clearly a better fit and more appropriate model for the data.

The set of MRAD values fell within a fairly narrow range, so an analysis using extreme value theory does not seem warranted. Nonetheless, if other researchers believe that applying other statistical techniques to these data could yield additional insights, they should feel free to publish their findings.

Xiao Dong, Brandon Milholland and Jan Vijg

James F Fries

2:56 p.m., 10 Oct 16 (UTC) | Link

This is a really interesting topic. The discussions around this subject, however, have become polarized and repetitive. It’s a continuation of the same argument and overreactions from the same researchers.

115 is probably a closer number the the lifespan limit. People aren’t really living longer - at least not in the last 40 to 50 years. A few people live to 115, and many more to 110 years old. That says something pretty solid. If somebody is not only out there on the edge of a gaussian curve, but is seven to eight years farther than anyone else, it defies the laws of statistics. It doesn’t mean it couldn’t happen, but it is unusual. Jeanne Calment may be a very clever case of age exaggeration. Either way, you can’t really say anything scientific about a single outlier.

Leonid Gavrilov

1:12 a.m., 16 Oct 16 (UTC) | Link

Dear Brandon Milholland,

Thank you for your interesting comments on your paper "Evidence for a limit to human life span", Dong et al., Nature 2016.

May I ask some questions regarding your Figure 1d, which presents the relationship between calendar year and the age that experiences the most rapid gains in survival:

  1. How do you measure the gains in survival in this particular case: as a difference between the numbers of survivors over time, or as a difference between the LOGARITHMS of the numbers of survivors over time? Or something else?

  2. What time intervals do you use, when you measure the gains in survival over time: just one year time interval (data for two close calendar years, say years 1981 and 1982, for example)? Or do you use longer time intervals?

Please advise. Thank you!

P.S.: By the way, you may enjoy our related published study, which explains why the chances for longevity records are much smaller than they were assumed earlier: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4342683/

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