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subject of this section is how to calculate life expectancy and
how to adjust it for serious co-morbid illness.
First, what is life
expectancy? It is the average length of life remaining to a person.
The life expectancy for an average person of a given age is known
from studies of the distribution of lengths of life in large populations.
It is an empirical observation, and there are tables from which
to obtain life expectancy of a person adjusted for age, race,
and gender.
The number of people
remaining in an aging cohort is also an empirical observation.
However, several mathematical functions, when graphed, describe
a curve that is a good approximation of the curve that shows the
number of survivors in a cohort. Ideally, the curve obtained by
plotting the mathematical function would be exactly the same as
the curve showing the number of survivors. One of these is the
Gompertz Function, which is hard to work with mathematically.
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