On Mean time of Survival of URLs

[JQ Johnson]

It should be noted that the research by Chankhunthod et al actually
measured the distribution of AGE of pages, not their mean lifetime.  As
anyone who has looked at actuarial statistics knows, these are very
different concepts, even in steady state populations.

By the way, as the age of the web as a whole increases, "mean" will become
an increasingly bad statistic to use for page lifetimes, since the mean
will be dominated by that small subset of pages that have been around from
the beginning.  Median lifetime and median age are much more useful
statistics for most purposes.