The charts provided offer a view of the Big Three from June 2007 through March 2008 for both market share and search volume, using stats from comScore, Nielsen, Hitwise and even Compete. And while some trends (i.e. Google retaining its search market dominance) were obvious, what became clearer was that the measurement firms' methodologies and stats were often quite different.
For example, Google came out on top for market share and number of searches. But while comScore and Compete peg the average volume of searches on Google in the 5 and 6.5 billion range, Nielsen reports a much lower average of about 4.5 billion queries.