"If the bars are close together, it suggests that the reported sizes given by the search engine are indeed correct.

If the "Reported" bar is higher than the "Estimated" bar, it suggests that the reported size for that search engine is inflated. It could also indicate that the research was not correct for that search engine.

Where the "Estimated" bar is higher than the "Reported" bar is higher, it suggests that the research may not have been correct for that search engine, or that the search engine itself underrepresented its index."

Sullivan, D. Search Engine Watch. 2000. www.searchenginewatch.com

Sullivan, D. (January 30, 1999) "Search Engine Sizes" http://www.searchenginewatch.com