Comparison of major web search engine overlap: 2005 and 2007

This paper provides preliminary results from a study examining the overlap among results retrieved by four major Web search engines for a large set of more than 19,332 queries. Previous studies show the lack of overlap in results returned by Web search engines for the same queries. Our large-scale study measured the overlap of first page results (both non-sponsored and sponsored) across four major Web search engines - Google, Live, Ask, and Yahoo! - using a large number of randomly selected Infospace, Inc queries from April 2007. We then compared the results to results retrieved for the same queries from the meta-search engine Dogpile.com. The percent of total results unique to only one of the four major Web search engines was 88.3 percent, with 8.9 percent of total search results found on two of the four Web search engines, 2.2 percent on three engines and 0.6 percent of results found across all four Web search engines. This level of Web search engine overlap is smaller than data from July 2005 and reflects the growing differences in Web search engines retrieval and ranking results. Results point to the value of meta-search engines in Web retrieval to overcome the biases of individual search engines.