That's consistent with most of those studies. The next paragraph does an interesting experiment showing a very conservative rate of 3% per year: >My specific t

That's consistent with most of those studies. The next paragraph does an interesting experiment showing a very conservative rate of 3% per year: >My specific target date is 2070, 60 years from now. As of 10 March 2011, gwern.net has around 6800 external links (with around 2200 to non-Wikipedia websites)4. Even at the lowest estimate of 3% annual linkrot, few will survive to 2070. If each link has a 97% chance of surviving each year, then the chance a link will be alive in 2070 is 0.972070−2011=0.16 (or to put it another way, an 84% chance any given link will die). The 95% confidence interval for such a binomial distribution says that of the 2200 non-Wikipedia links, ~336-394 will survive to 20705. If we try to predict using a more reasonable estimate of 50% linkrot, then an average of 0 links will survive (0.502070−2011×2200=1.735×10−16×2200≃0). It would be a good idea to simply assume that no link will survive.