From: Eugen Leitl (eugen@leitl.org)
Date: Sat May 11 2002 - 05:48:51 MDT
On Fri, 10 May 2002, Hal Finney wrote:
> First, although the article is only available to subscribers,
> there is a lot of material on line at
> http://www.sciencemag.org/cgi/content/full/296/5570/1029/DC1.
http://www.sciencemag.org/cgi/content/full/296/5570/1029
DEMOGRAPHY:
Enhanced: Broken Limits to Life Expectancy
Jim Oeppen [HN8] and James W. Vaupel [HN9]*
Is life expectancy [HN1] approaching its limit? Many--including
individuals planning their retirement and officials responsible for health
and social policy--believe it is. The evidence suggests otherwise.
Consider first an astonishing fact. Female life expectancy in the
record-holding country has risen for 160 years at a steady pace of almost
3 months per year [Fig. 1 and suppl. table 1 (1 )]. In 1840 the record was
held by Swedish women, who lived on average a little more than 45 years.
Among nations today, the longest expectation of life--almost 85 years--is
enjoyed by Japanese women [HN2]. The four-decade increase in life
expectancy in 16 decades is so extraordinarily linear [r2 = 0.992; also
see suppl. figs. 1 to 5 (1 )] that it may be the most remarkable
regularity of mass endeavor ever observed. Record life expectancy has also
risen linearly for men (r2 = 0.980), albeit more slowly (slope = 0.222):
the gap between female and male levels [HN3] has grown from 2 to 6 years
(suppl. fig. 2).
Figure 1
Fig. 1. Record female life expectancy from 1840 to the present [suppl.
table 2 (1 )]. The linear-regression trend is depicted by a bold black
line (slope = 0.243) and the extrapolated trend by a dashed gray line. The
horizontal black lines show asserted ceilings on life expectancy, with a
short vertical line indicating the year of publication (suppl. table 1).
The dashed red lines denote projections of female life expectancy in Japan
published by the United Nations in 1986, 1999, and 2001 (1): It is
encouraging that the U.N. altered its projection so radically between 1999
and 2001.
In addition to forewarning any looming limit to the expectation of life,
trends in best-practice life expectancy provide information about the
performance of countries. The gap between the record and the national
level is a measure of how much better a country might do at current states
of knowledge and demonstrated practice. Although rapid progress in
catch-up periods typically is followed by a slower rise, life-expectancy
trajectories do not appear to be approaching a maximum (Fig. 2).
Figure 2
Fig. 2. Female life expectancy in Chile, Japan, New Zealand (non-Maori),
Norway, and the United States compared with the trend in record life
expectancy.
The linear climb of record life expectancy suggests that reductions in
mortality should not be seen as a disconnected sequence of unrepeatable
revolutions but rather as a regular stream of continuing progress (2, 3).
Mortality improvements [HN4] result from the intricate interplay of
advances in income, salubrity, nutrition, education, sanitation, and
medicine, with the mix varying over age, period, cohort, place, and
disease (4 ). Before 1950, most of the gain in life expectancy was due to
large reductions in death rates at younger ages. In the second half of the
20th century, improvements in survival after age 65 propelled the rise in
the length of people's lives. For Japanese females, remaining life
expectancy at age 65 grew from 13 years in 1950 to 22 years today, and the
chance of surviving from 65 to 100 soared from less than 1 in 1000 to 1 in
20 (1). The details are complicated but the resultant straight line of
life-expectancy increase is simple.
World life expectancy more than doubled over the past two centuries, from
roughly 25 years to about 65 for men and 70 for women (4 ). This
transformation of the duration of life greatly enhanced the quantity and
quality of people's lives. It fueled enormous increases in economic output
and in population size, including an explosion in the number of the
elderly [HN5] (5, 6 ). Although students of mortality eventually
recognized the reality of improvements in survival, they blindly clung to
the ancient notion that under favorable conditions the typical human has a
characteristic life-span. As the expectation of life rose higher and
higher, experts were unable to imagine its rising much further. They
envisioned various biological barriers and practical impediments. The
notion of a fixed life-span evolved into a belief in a looming limit to
life expectancy.
Ultimate Expectations of Life
In 1928, Louis Dublin quantified this consensus (7). Using U.S. life
tables as a guide, he estimated the lowest level to which the death rate
in each age group could possibly be reduced. His calculations were made
"in the light of present knowledge and without intervention of radical
innovations or fantastic evolutionary change in our physiological make-up,
such as we have no reason to assume." His "hypothetical table promised an
ultimate figure of 64.75 years" for the expectation of life both for males
and for females. At the time, U.S. life expectancy was about 57 years.
Because Dublin did not have data for New Zealand, he did not realize that
his ceiling had been pierced by women there: in the non-Maori life table
for 1921, female life expectancy is 65.93 years [Fig. 1 and suppl. tables
1 and 2 (1)].
Marshalling methods and arguments strikingly similar to Dublin's,
Olshansky et al. in 1990 and again in 2001 [HN6] assess the life
expectancy that could be attained if age-specific death rates could be
reduced by amounts that are not "implausible," "overly optimistic," and
"highly unlikely" (8, 9 ). In 1990, they asserted that life expectancy
"should not exceed ... 35 years at age 50 unless major breakthroughs occur
in controlling the fundamental rate of aging." This cap, however, was
surpassed by Japanese females in 1996.
Other scholars tried various stratagems to seize life expectancy heights
that they could not conceive of being surmounted (1). Although some of the
more recent ostensible limits have not yet been exceeded, those from
Dublin in 1928 to Olshansky et al. in 1990 have been broken, on average 5
years after publication (Fig. 1 and suppl. table 1).
Better Forecasts
The ignominious saga of life-expectancy maxima is more than an exquisite
case for historians intrigued by the foibles of science. Continuing belief
in imminent limits is distorting public and private decision-making.
Forecasts of the expectation of life [HN7] are used to determine future
pension, health-care, and other social needs. Increases in life expectancy
of a few years can produce large changes in the numbers of the old and
very old, substantially augmenting these needs (5, 6 ). The officials
responsible for making projections have recalcitrantly assumed that life
expectancy will increase slowly and not much further (10 ). The official
forecasts distort people's decisions about how much to save and when to
retire. They give politicians license to postpone painful adjustments to
social-security and medical-care systems (11).
Officials charged with forecasting trends in life expectancy over future
decades should base their calculations on the empirical record of
mortality improvements over corresponding spans of the past (2, 3 ).
Because best-practice life expectancy has increased by 2.5 years per
decade for a century and a half, one reasonable scenario would be that
this trend will continue in coming decades. If so, record life expectancy
will reach 100 in about six decades. This is far from eternity: modest
annual increments in life expectancy will never lead to immortality. It is
striking, however, that centenarians may become commonplace within the
lifetimes of people alive today (12).
Life expectancy can be forecast by considering the gap between national
performance and the best-practice level (Fig. 2). The U.S. disadvantage
varied from a decade in 1900 to less than a year in 1950 and about 5 years
in 2000 (Fig. 2). If the trend in record life expectancy continues and if
the U.S. disadvantage is between a year and a decade in 2070, then female
life expectancy would be between 92.5 and 101.5, considerably higher than
the Social Security Administration's forecast of 83.9 published in 1999 (1
). An alternative method for forecasting life expectancy is to analyze the
rapidity of improvement in age-specific death rates over many decades and
then to use this information to project death rates over coming decades
(2, 3). The official Japanese forecast, issued in 1997, of life expectancy
(for males and females combined) in 2050 is 82.95 (1 ). Projections based
on the decline in death rates in Japan since 1950 result in a life
expectancy some 8 years longer, 90.91, with a 90% confidence range from
87.64 to 94.18 (3).
Declines in mortality might be systematically slower than in the past. On
the other hand, biomedical research may yield unprecedented increases in
survival. Given the extraordinary rise in best-practice life expectancy
and the demonstrated nearsightedness of expert vision, the central
forecast should be based on the long-term trend of sustained progress in
reducing mortality.
In their quest to impose a cap on average longevity, students of mortality
ignored essential research questions. Major changes in life expectancy
hinge on improvements in survival at advanced ages, but comprehensive
analysis of the substantial reductions since the mid-20th century in death
rates after age 80 first flourished in the 1990s (1, 13 ). Hypothesized
biological barriers to longer life-spans also first received systematic
attention (and refutation) a decade ago (1, 14-16). The impact of
continuing mortality improvements on life expectancy attracted empirical
(12) and theoretical attention (17) in the late 1980s, with refined
methods developed over the past decade (1-3).
Three Findings
This mortality research has exposed the empirical misconceptions and
specious theories that underlie the pernicious belief that the expectation
of life cannot rise much further. Nonetheless, faith in proximate
longevity limits endures, sustained by ex cathedra pronouncement and
mutual citation (1, 8, 9 ). In this article we add three further lines of
cogent evidence. First, experts have repeatedly asserted that life
expectancy is approaching a ceiling: these experts have repeatedly been
proven wrong. Second, the apparent leveling off of life expectancy in
various countries is an artifact of laggards catching up and leaders
falling behind. Third, if life expectancy were close to a maximum, then
the increase in the record expectation of life should be slowing. It is
not. For 160 years, best-performance life expectancy has steadily
increased by a quarter of a year per year, an extraordinary constancy of
human achievement.
References and Notes
1. Supplemental material--including data sources and additional
references--is available on Science Online at
http://www.sciencemag.org/cgi/content/full/296/5570/1029/DC1. Life
expectancy is the mean age at death under current mortality conditions.
2. R. D. Lee, L. Carter, J. Am. Stat. Assoc. 87, 659 (1992).
3. S. Tuljapurkar, N. Li, C. Boe, Nature 405, 789 (2000) [Medline].
4. J. Riley, Rising Life Expectancy: A Global History (Cambridge Univ.
Press, Cambridge, 2001), 243 pp [publisher's information].
5. L. G. Martin, S. H. Preston, Demography of Aging (National Academy
Press, Washington, DC, 1994) [publisher's information].
6. R. W. Fogel, D. L. Costa, Demography 34, 49 (1997) [Medline].
7. L. I. Dublin, Health and Wealth (Harper, New York, 1928), 361 pp.
8. S. J. Olshansky, B. A. Carnes, C. Cassel, Science 250, 634 (1990)
[Medline] [JSTOR].
9. S. J. Olshansky, B. A. Carnes, A. Désesquelles, Science 292, 1654
(2001).
10. N. Keilman, J. Offic. Stat. 12, 245 (1997).
11. J. W. Vaupel, Washington Q. 23, 197 (2000) [Summary/full text].
12. J. W. Vaupel, A. E. Gowan, Am. J. Public Health 76, 430 (1986)
[Medline].
13. V. Kannisto, J. Lauritsen, A.R. Thatcher, J.W. Vaupel, Pop. Dev.
Rev. 20, 793 (1994).
14. J. R. Carey, P. Liedo, D. Orozco, J. W. Vaupel, Science 258, 457
(1992) [Medline] [JSTOR].
15. J. W. Curtsinger, H. H. Fukui, D. Townsend, J. W. Vaupel, Science
258, 461 (1992) [Medline] [JSTOR].
16. J. W. Vaupel et al., Science 280, 855 (1998).
17. J. W. Vaupel, Pop. Stud. 40, 147 (1986) [Medline].
18. Funded by the Max Planck Society and the U.S. National Institute on
Aging (AG-08761). We thank V. Kannisto, P. Laslett, S. Horiuchi, R. D.
Lee, S. Leek, H. Maier, M. Luy, R. Rau, Y. Saito, S. Tuljapurkar, K. W.
Wachter, and J. R. Wilmoth for their assistance.
J. Oeppen is with the Cambridge Group for the History of Population and
Social Structure, Cambridge University, Cambridge, CB2 3EN, UK. He is
associated with, and J. W. Vaupel is at, the Max Planck Institute for
Demographic Research, Doberaner Strasse 114, D-18057 Rostock, Germany.
*To whom correspondence should be addressed. E-mail: jwv@demogr.mpg.de
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