Thank you. I suspected the infant mortality rate had something to do with it (although I did not understand the formula - what is $delta$x?). People like to make sensational statements like "the average person only lived 40 years". If you are honest, you will spell out WHAT you are averaging.
I must guard against this also. I tend to use half-truths to justify making a point.
If the point is valid, it deserves to be justified by truth. If half-truths are necessary, then my point is invalid.