ofinformation ontheweb: Analyzing citations contained in research articles

We analyze the persistence of information on the web, looking at the percentage of invalid URLs contained in academic articles within the CiteSeer database. The number of URLs contained in the papers has increased from an average of 0.06 in 1993 to 1.6 in 1999. We found that a significant percentage of URLs are now invalid, ranging from 23% for 1999 articles, to 54% for 1994. We also found that for almost all of the invalid URLs, it was possi- ble to locate the information (or highly related information) in an alternate location, primarily with the use of search engines. How- ever, the ability to relocate missing information varied according to search experience and effort expended. Citation practices sug- gest that more information may be lost in the future unless these practices are improved. We discuss persistent URL standards and their usage, and give recommendations for citing URLs in research articles as well as for finding the new location of invalid URLs.