In reply to:


but I meant to say that the standard deviation of people's lifetimes is much greater in developing countries than in established countries.



Hey, Bitt, I can tell, its not your day to day.

I know what you mean with the above sentence, but what you actually said is pretty much like the earlier comment about people having a tendancy to die throughout their lives.

I don't need to point out, but I will anyway, for the benefit of our other readers [you know who you are :-)) ] that the word "standard" in standard deviation is there, as this statistical concept lets you can compare variability of actual numbers (like age of death) across different populations [e.g. developed versus undeveloped world].

The actual gauge of the variability in a statistical measure is the variance - (of which the standard deviation is the square root and so relates to the variance, but it is subtly a different measurement).

What you really meant to say is the average (or mean) age of death will probably be much be lower in a developing country and the "variance" around this average figure will also be quite large due to the existence lots of early deaths in childhood and also due to the presence of a few very old people.

As compared to the west say where much fewer numbers of children die and the aged tend to live longer lives as well.

In fact, if you look at the "average life expectancy" statistic that gets bandied around from time to time, you will note how the Average life expectancy at birth in the 1800's in the UK was about 43 and now its 74 or something and rising.
[and its also quoted as only 35 or so for cavemen in some books I've read].

That doesn't mean that most people died at 43 in the UK in 1800's - although thats the meaning you would take at first glance.

All it says that if you average the age of death across everyone born in any one year in the 1800's that average value was 43 years old, of course many people live longer than that, and many,many more children died before they reached say, 5 years old and these figures tend to increase the variability of the age of death figure.

What that statistic also doesn't show (unless you dig a lot further) is that most of the improvement in this average life expectancy figure since the 1800's was gained through reducing dramatically the incidence of death in early childhood [so-called infant mortality].

And this has the dramatic effect of pushing the average age at death right up to 74 or whatever it is now.

Sure the fact that we live longer helps too, but thats mainly due to the fact that adding values above the average figure to a set of values, pushes the mean/average value higher.

i.e. not dying before you exceed the current average "age at death" figure helps push the average age of death figure higher.