Cookie-based Data Likely Overstating Uniques by 150% : Comscore

Comscore released a new cookie study that is pretty strong evidence of the further erosion of the ability to use cookies to track anything unique. President/CEO Dr. Magid Abraham says that with 7% of computers accounting for 35% of all cookies "just one set of 'eyeballs' at the site may be counted as 10 or more unique visitors over the course of a month. The result is a highly inflated estimate of unique visitors for sites that rely on cookies to count their audience." This also goes for adserver counts of unique users that were served an ad. One more observation worth noting is that 3rd party cookies are deleted at no higher rate than 1st party cookies - contrary to a prevailing rule of thumb that holds that users who utilize security programs to keep their PCs clean are more likely to find 3rd party cookies invasive and choose to delete them, as opposed to 1st party cookies set directly by a friendly web site. Bottom line, if the methodology was correct, Comscore shows that many web site and ad server logs can exaggerate the audience by a factor as high as 2.5, or an overstatement of 150 percent.