The debate about the most efficient and relevant metrics in the digital world is still going on. Recently comScore has published a study about the impact of cookie deletion behavior on website audience measurement and the reach and frequency of online advertising campaigns in the Latin American market. The study finds that without proper adjustments, site-server estimates can overstate audience size by factor of up to 2.5x The study addresses the key sources of discrepancy between server-based and panel-based data and reveals that cookie deletion can lead to large overstatements in server logs’ measurement of the size of online audiences. As we said before, 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.

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 which can arrive to an overstatement of up to 150 percent. 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.  The actual magnitude of the overstatement depends on the frequency of visitation to the site or exposure to the campaign.

The analysis of cookie deletion patterns across each country revealed similar consumer behaviors across markets. 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.

Brazil

The study found that 32 percent of Brazil’s Internet audience cleared their first-party cookies during the month, while third-party cookie deletion rates were even higher at 43.3 percent. 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 Unique Visitors in Brazil by a factor of up to 2.4x. Similarly, the study found that an ad-server system which uses cookies to track the reach and frequency of an online campaign will overstate reach by a factor of up to 5.5x and understate frequency to the same degree.

Mexico

The study found that 31 percent of Mexico’s Internet audience clears their first-party cookies, while third-party cookie deletion rates were even higher at nearly 43 percent. Accordingly, cookie-based counting methods will typically overstate the true number of Unique Visitors in Mexico by a factor of up to 2.4x. Similarly, the study found that an ad-server system which uses cookies to track the reach and frequency of an online campaign will overstate reach by a factor of up to 4.8x and understate frequency to the same degree.

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