A UIUC study is casting doubts on Yahoo!s reported number of 19,2 billion websites in their index. In this study, they tested the number of found websites with the English Ispell-wordlist. The Yahoo! average should be more than twice that of Google (8,1 billion websites). Seeing how both searchengines will only return a maximum of 1000 results, only those terms that had less than 1000 results were tested for.
The surprising result of this study is that Google had, on average, 166% more results than Yahoo. Yahoo returned for only 3% of the 10.012 checked terms more results than Google.