I came across a very interesting resource today -- the Chesapeake Project Legal Information Archive -- and the just-released results of a study they did on archiving legal resources on the web:
Not too surprisingly, the second highest class of domain to where resource loss is found is .edu, after .info. Academic institutions are not always very conscientious about preserving access to their content, and with their academic term structure and the movement of faculty between institutions, web content on .edu sites is highly variable in its longevity. I don't see a characterization of how old the resources are that they harvested -- that can be very difficult to identify -- but it is a high percentage of bitrot, and there was quite an increase from the end of the first year to the end of the second year.
The Chesapeake Project Legal Information Archive has released a comprehensive report evaluating its digital preservation efforts during the project's two-year pilot phase.
The project evaluation reveals that nearly 14 percent — or approximately one in seven — of the online publications archived between March 2007 and March 2009 have already disappeared from their original locations on the Web but, due to the project's efforts, remain accessible via permanent archive URLs. A similar analysis in 2008 showed that slightly more than 8 percent of archived titles had disappeared from their original URLs, demonstrating a dramatic increase in "link rot," or inactive URLs, among archived content over the past year.
During the two-year pilot phase, the libraries participating in the project archived more than 4,300 digital objects and tracked more than 177,000 visits to www.legalinfoarchive.org, the home of The Chesapeake Project's digital archive collections. Users of the project's Web site visited from educational, government, and military institutions in the United States, as well as from countries abroad throughout the Americas, Europe, the Middle East, Asia, Africa, Australia, and the Pacific Islands.
Download the PDF of their report.