Search engine results over time-a case study on search engine stability

This paper examines the performance of search engines over time. The performance is not as expected: search engines loose information, relevant URLs that were retrieved at a given time by a certain search engine, were not retrieved by the same search engine at a later time, although they continued to exist and to be relevant. A closer examination of the these URLs revealed that not only URLs were dropped, but content was also lost for a large portion of these URLs: no other URL retrieved by the search engine contained the same information. As far as we know this aspect of the performance of search engines has not been thoroughly studied before. The problem is investigated through a case study, using the search phrase "informetrics OR informetric". The searches were carried out in one month intervals during a five months period between January and June 1998. An additional search round and comparison were carried out on June 1999. The six largest search engines at the time were examinedPeer reviewe