Frequent Cookie Deletion by 3 out of 10 U.S. Internet Users Leads to Overstatements in Audience Sizes by a Factor as High as 2.5comScore released a study that analyzed the validity of using cookie-based data to measure unique visitors; moreover, to estimate the number of unique views of an advertisement. The results? Server logs that count unique cookies to measure unique visitors may be off as high as 2.5, for an overstatement of 150 percent.
I set my browser to clear cache, cookies and temporary Internet files each time I close the browser. Do you clear your cookies? Why or why not?