From: Hal Finney (hal@finney.org)
Date: Fri May 10 2002 - 16:27:42 MDT
Harvey writes, about the Nature article:
> > Study Indicates No Natural Limit To Life Expectancy
>
> I wish this were true, but I think this analysis is flawed.
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.
(You might have to do a free login; I used cypherpunks/cypherpunks.)
It shows what is the main point of the article, which is that if you
plot the maximum (female) life expectancy of all countries in the world
on a given date, the resulting curve is very close to a straight line.
I briefly glanced at the original article at the library this afternoon,
and its chart included annotations showing historical predictions of
limits on the average life span. You can see the data in "Supplemental
Table 1" in the link above. These predictions were generally a few years
or a decade above the then-current average. Historically, demographers
have predicted that average life span would not grow much above what it
was at the time. The point of the article is that these predictions have
generally been false, and so they will probably be false in the future.
Instead, extrapolating the straight line forward implies a steady increase
in average life span with no inherent maximum.
The article is actually titled "Broken Limits to Life Expectancy" and
so it mostly plays up the erroneous predictions of the past rather than
strongly arguing that there is literally no limit to life expectancy in
the future.
Harvey further wrote:
> There are two groups of deaths.
>
> Group one is premature deaths. These are caused by nutritional
> deficiencies and disease (and accidents). These are being addressed by
> medical breakthroughs. Many such deaths are being prevented, so people
> in this group are living longer. This makes the average lifespan go
> up. However, this group is not affected by old age. They die due to
> other causes before old age kills them.
>
> Group two are non-premature deaths. Such people live a full natural
> lifespan and die of old age. Old age has not been solved by medical
> breakthroughs (yet). Statistics show that maximum lifespans are not
> increasing (yet). People who live to the end of their natural lives are
> not living longer. However, they are not decreasing either, so the
> average lifespan still goes up. This group is always affected by old
> age. They avoid other causes of death and always reach old age at the
> end of their life.
I'm not sure you can strictly separate these two. Nobody gets "old age"
on their death certificate. People die because of specific failures in
the mechanisms that makes up the body. There may be multiple simultaneous
failures, but theoretically if you could have fixed those problems they
would have lived at least a bit longer. In other words, what we call
"old age" is a complex of diseases as the body's systems fail, and it's
one or more of those diseases that kills you.
> The study combined these two groups and only looked at increases in
> average lifespan. By only looking at increases, they were only seeing
> data from group one. Group two did not have any increases, and
> therefore did not influence the statistical increases being studied.
I don't think so; average life span is calculated over everyone. If you
did have two groups, and group 1's average life span rose 5 years while
group 2's stayed the same, then the average life span change for the
population as a whole would be less than 5 years, because of the influence
of group 2 on the average. So group 2 does influence the statistics of
the increase.
> In
> other words, all the statistical analysis really only was done on group
> one. Group two had no affect on the data being measured. When the
> study concluded that old age didn't exist, what they really were saying
> is that none of the people seeing lifespan increases (group one)
> indicated any limitations from old age. This is correct.
The study concluded that old age didn't exist? I didn't have time to
read the article closely but that would be a strange claim to make.
> Had they
> actually done statistical analysis on people who weren't seeing lifespan
> increases (group two), they would have found the opposite conclusion.
> All of them were being limited by old age. Within this group they would
> have concluded that only old age exists (and no other causes of death
> exists).
>
> Basically, this study accidentally measured a smaller subset of people
> and then misapplied those measurements to all people. They also
> measured average numbers and misapplied these to all individual members
> of the group. Both of these are invalid statistical methods. This
> study didn't really prove that old age doesn't exist. It proved that
> old age doesn't exist for people who die prematurely. It also proved
> that none of our increases in lifespan that we have seen have involved
> old age.
I didn't read the article (in the brief time I had) as making these
kinds of claims. What I saw was evidence that previous predictions of a
ceiling on average life span had been wrong, and a prediction that simply
extrapolating the linear growth forward was more likely to be correct.
By their figures of about 1/4 year per year in growth of average life
span, it will take 140 years before we hit the 120 year "ceiling".
I suspect the authors might be willing to entertain that as a limit to
their methodology; I don't think they would have expected to be able to
make a prediction that would hold past a century and a half.
In any case, as Extropians I presume we all agree that these kinds of
predictions are nonsense. We confidently expect options for effectively
unlimited lifespans within the next century. The straight line may have
worked well in the past, but it's about to take a great leap upwards.
Hal
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