These results also proved that the most popular search engines did not produce accurate results for the initial search which may contain some inherent errors that are not easily observed/detected or documented. Literature on search strategies, as well as the actual search engine Web pages, inform the user that the results may vary among diferent search engines. However, this information does not mention that the results produced by each search engine may vary over a period of days due to the undocumented refnement of the same keywords