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The Impact of Cookie Deletion - Inflated Audience Reports

Posted on 5.08.2011

Comscore today released a study which address the key sources of discrepancy between server-based and panel-baed data and reveals that cookie deletion can lead to large overstatements in server logs measurement of the size of online audiences.

According to Comscore, “Without appropriate adjustments, server-based audience reports can be inflated up to 2.5 times the actual number of unique visitors.”

The report, which analyzed behaviors in Latin America (Argentina, Brazil, Chile, etc.), revealed that approximately 33 percent of Internet users delete their first-party (i.e. web site) cookies in a month. Third-party (i.e. ad server) cookie deletion rates are even higher than first-party deletion rates, with nearly 43 percent of Internet users deleting their third-party cookies in a month.

The study also found that an ad-server system which uses cookies to track the reach and frequency of an online campaign will overstate monthly reach by a factor of up to 5.2x and understate frequency to the same degree.


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