# What does life expectancy measure exactly

I’m confused about life expectancy. What is it exactly, the number of years you’re expected to live at birth?

What about countries which have higher child & infant mortality and therefore life expectancies of about 40 years. Does that mean a minority of people die young, but everyone else lives to be about 70-80?

What corrections for life expectancy are there when you subtract lives lost to infant and childhood mortality? Would that increase life expectancy in countries with an expectancy of 40 to about 70?

Life expectancy can be calculated for any age, although it is most frequently given “at birth.”

From this life table you can see that in the US, life expectancy for males is 74.14 at age zero, but at age 50 a male can expect to live another 27.85 years, for a total life expectancy of 77.85 years.

The difference is relatively small because infant mortality in the US is low. In countries with a very high infant mortality rate, where life expectancy at birth may be in the 40s, life expectancy at age 50 is likely to be in the 60s or 70s.

There is one crucial assumption (see end note of the table that Colibri linked to.) I interpret this end note to mean that the life expectancies assume e.g. the probability of a person born on 1 January 2001 dying during the year 2071 equals the probability of a person born in on 1 January 1931 dying in 2001. That’s assuming a lot IMO.

Yes, but that’s not useful to know unless you know what “expected” means in this context. Wiki gives a pretty good overview.

It would have to be a pretty significant minority–maybe even a majority–to drive the number that far down.

The easiest correction is to work with the population that’s lived long enough to avoid high infant mortality rates. I don’t know exactly when the drop off is, but if you calculate your life expectancies from the first birthday, you’ll probably get a very different picture.