You have done an exploratory experiment using ExpectedLifeTime.nb in class last Saturday.
You should have seen that the longevity was Type I (60.43), Type II (21.72), and Type III (19.28), in that order.
More interesting than the longevity comparison is comparison of the relationship between the longevity and the length of remaining life at other ages between each type.
I didn't explain how to get life expectancy at an arbitrary age
in the class. The life expectancy of an individual at -age is
or, if you can define
as any continuous function,
" in eq. is for mathematical convenience. Realistically, this is the age at which they will live the longest.
Think about why the equations look like this form. I hope you are convinced.
Let's look at longevity and life expectancy, for exammple, at age-20 (
|Type I||Type II||Type III|
|Life expectancy at age-20||40.79||21.72||21.89|
In Type I, a newborn has a longer remaining life than a 20-year-old adult. In Type II, the remaining life for a newborn and for an individual of age-20 is the same. In Type III, a age-20 adult has a longer remaining life than a newborn.
At first, the pattern for type 1 seems to follow our intuition, and we may wonder about the pattern for type II and type III. Perhaps, with a little thought, you will be able to understand why this happens.
Even so, let's examine why this is so below. The table shows some of the yearly values of the
We can derive other interesting parameters from
is the probability that a newborn is alive at age- . is the probability that an individual of age survives to age . is the probability that an individual of age die by age . is the complement of .
Examples for type I case
means that a newborn has a chance of survival at age-10. means that an age-10 individual has a chance of survival at age-11. means that an age-10 individual has 0.023...% chance of dying before reaching age-11.