Research has reported that about 10% of Web searchers utilize advanced query operators, with the other 90% using extremely simple queries. It is often assumed that the use of query operators, such as Boolean operators and phrase searching, improves the effectiveness of Web searching. We test this assumption by examining the effects of query operators on the performance of three major Web search engines. We selected one hundred queries from the transaction log of a Web search service. Each of

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... se original queries contained query operators such as AND, OR, MUST APPEAR (+), or PHRASE (" "). We then removed the operators from these one hundred advanced queries. We submitted both the original and modified queries to three major Web search engines; a total of 600 queries were submitted and 5,748 documents evaluated. We compared the results from the original queries with the operators to the results from the modified queries without the operators. We examined the results for changes in coverage, relative precision, and ranking of relevant documents. The use of most query operators had no significant effect on coverage, relative precision, or ranking, although the effect varied depending on the search engine. We discuss implications for the effectiveness of searching techniques as currently taught, for future information retrieval system design, and for future research.