Latin America: Cookie deletion leads to severe audience over-estimates

May 27, 2011 | Latin America

There is a discrepancy between server-based and panel-based data and reveals that cookie deletion that can lead to large overstatements in server logs’ measurement of the size of online audiences, according to a new study in Latin America. The study, from comScore, found that without appropriate adjustments, server-based audience reports can be inflated up to […]

There is a discrepancy between server-based and panel-based data and reveals that cookie deletion that can lead to large overstatements in server logs’ measurement of the size of online audiences, according to a new study in Latin America. The study, from comScore, found that without appropriate adjustments, server-based audience reports can be inflated up to 2.5 times the actual number of unique visitors. The study analyzes behaviors in Latin America, including individual market analysis for Argentina, Brazil, Chile, Colombia, Mexico, Peru and Venezuela.


The report revealed the following key findings for the Latin America market:
– 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.
– “Serial cookie deleters” have a profound impact on inflating site-server logs because they represent a small percentage of computers, but a very large share of observed cookies.
– Because of the high rate of cookie deletion, a server-centric measurement system which uses cookies to measure the size of a site’s visitor base will typically overstate the true number of monthly unique visitors by a factor of up to 2.5x in Latin America.
Similarly, the study 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.
– Comparing cookie deletion rates across individual Latin America markets, the study reported third-party cookies being deleted by 42-45 percent of computers per month, with first-party deletion rates in excess of 30 percent in each country.
– Argentina exhibited the highest rates of cookie deletion for both first-party and third-party cookies at 36 percent and 45 percent of Internet users, respectively.
To download the full report, The Impact of Cookie Deletion on Site-Server and Ad-Server Metrics in Latin America: An Empirical comScore Study, click here.

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