I have been thinking about the data set even more and think I might now understand why the authors data makes it look like karateka are dieing earlier than expected, and why we should be sceptical about it. It is a little bit complicated so you will have to bear with me.
The book does contain a section on "understanding how longevity is measured". This section contains a chart, the only actual data in this section, for life expectancy for Americans. I have coped the first line below which is indicitve of all the lines:
Calendar period 1850 (I assume this is year of birth)
Age: 0 10 20 30 40 50 60 70 80
Expected years of life remaining: 38.3 48 40.1 34 27.9 21.6 15.6 10.2 5.9
So, if you were born in 1850 and you live to be 10yrs old you will then expect to live to be 58. If you live to be 20yrs old then you can expect to live to 60.1 yrs. If you live to be 60 you would then expect to live to be 75. So the longer you live, the longer still you might be expected to live.
It seems to me that adopting this approach makes it almost impossible for someone to die after their expected date of death. I suspect that this is the real reason why almost none of the 118 examples in the book actually managed it.
The following illustrates my thinking further:
The" age at death" of karateka chart contains 3 people who were all born in 1889.
It is important to undersand that by the time the 3rd person had reached 97 almost the entirety of humanity born in 1889 had already died. It therefore seems to me ludicrous to assert that this individual died 2yrs earlier than expected. He was not someone who died early, but was in fact someone who had extraordinary longevity.
It therefore follows, that for me at least, it seem preposterous to cite one of the longest lived individuals born in 1889 as evidence of people dieing early as a result of practising karate.
When I reflect upon this comment, coupled with my earlier one, I find myself compelled to the view that the author of the book has not established a credible link to the practice of karate and shortened lifespans.
That's statistics at play. They system your book describes for calculating life expectancy is commonly used in certain industries, but not for the purpose of calculating the age somebody *should* live to. Rather, it is used to calculate financial risk. The formula is commonly used by pensions companies to estimate how much they are likely to have to pay out, and therfore how much someone needs to pay in. If someone lives to 70, chances are they look after themselves, so will live to 80. An 80 year old must really look after himself so could live to 90 and so on. That's useful for making financial risk assessments, but absolutely useless for calculating life expectancy for any other reason.
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