Answer: On Mean time of Survival of URLs -Reply

[Dan Lester]

Our own casual, non-scientific measures, are that about 3
percent of our links go bad each month.  We run
CyberSpyder monthly and that figure is reasonable for what
we have on our pages.  Of course many of the links checked
are internal ones that don't change, so the "outside links"
may break at 5 or 6 percent a month.  

I don't have a cite, but check out    http://www.hotbot.com for
potentially added information.  I went to their presentation on
their product at their offices during the ALA conference. 
Numbers were presented, but I candidly don't remember the
details.  If nothing else, you could email them for more info. 
HotBot makes a big point of keeping their database of links
cleaner than anyone elses, so they ought to have some
numbers, and might even give out solid information.  

Sorry for not noting details, but it was at end of a long day at
ALA and they DID have refreshments, and......well, you
know...

dan