Web Audience Measurement by Cookie Counting Considerably Overestimated

comScore recently released a study that analyzes the validity of using cookie-based data to measure unique visitors and to gauge the number of unique users that were served an ad by an ad server. The results indicate that Web site server logs that count unique cookies to measure unique visitors are likely to be exaggerating the size of the site's audience by a factor as high as 2.5, or an overstatement of 150 percent. >>Full Story

Thoughts// The accuracy of cookie-based data has always been in question, however this is one of the first reports to provide an estimate of how great the difference could be. While cookie-based the data does provide some good insight, users resetting their cookies causes problems with the accuracy of the data. At this point, this type of report does not affect how AOT reports web site statistics due to the fact that industry standards remain the same.