Researchers on Monday labeled as "suspicious" Yahoo Inc.'s claims that its search index is nearly twice as large as Google Inc.'s.
Yahoo last week crowed about the 20 billion items in its index, in an apparent attempt to flex a bit of marketing muscle over the search giant, which has 11.2 billion items. Yahoo, however, also acknowledged that the size of the index is only one factor in delivering quality search results.
But a study by researchers at the University of Illinois at Urbana-Champaign and the National Center for Supercomputing Applications found that on a random sample of 10,012 searches, Yahoo returned only 37.4 percent of the results of Google.
"It is the opinion of this study that Yahoo's claim to have a web index of over twice as many documents as Google's index is suspicious," the researchers said in a statement. "Unless a large number of the documents Yahoo has indexed are not yet available to its search engine, we find it puzzling that Yahoo's search engine consistently returned fewer results than Google."
Yahoo denounced the study, saying its methodology was flawed.
"The study cannot be used to determine how many documents are in the index," Yahoo spokesman Aaron Ferstman said. "It can simply be used to see how well the index returns documents."
The real test, in any case, is not how many items are in the index, but which search engine returns useful results to the user, Ferstman said. "What really matters ultimately is relevance."
In aggregate, Yahoo returned 146,330 search results, while Google returned almost three times as many at 390,595, the researchers said. Because the search engines deliver only up to a 1,000 results, the researchers used search terms that delivered less than a thousand results.
The study found that a user could expect, on average, to receive 166.9 percent more results using the Google search engine than Yahoo's. In fact, only in 3 percent of the cases did Yahoo return more results. In less than 1 percent of the cases did both search engines return the same number of results.
Researchers included Matthew Cheney, Mike Perry, and Orville Vernon Burton.