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23. Jan 2020

comScore Publishes White Paper on the Impact of Cookie Deletion on Website Audience Measurement in Australia

*Study Finds that Without Proper Adjustments, Site-Server Estimates can Overstate Audience Size by Factor of up to 2.7x*

Sydney, Australia, February 3, 2011 – comScore, Inc., a leader in measuring the digital world, today released its white paper, The Impact of Cookie Deletion on Site-Server and Ad-Server Metrics in Australia: An Empirical comScore Study. 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 servers’ measurement of the size of online audiences. Without appropriate adjustments, site-server measurement of the size of website audiences in Australia can be inflated by up to 2.7 times the actual number of unique visitors.

The report revealed the following key findings for the Australian market:

  • Approximately 28 percent of Internet users in Australia delete their first-party cookies in a month. Third-party cookie percentages are even higher, with nearly 37 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 unique visitors by a factor of up to 2.7x in Australia.
  • 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 5.7x and understate frequency to the same degree.
  • Comparing cookie deletion in Australia with other markets across the globe including the U.S., U.K., Brazil, France, Germany and New Zealand found that each country saw third-party cookies being deleted by approximately 30-40 percent of Internet users, with first-party cookies deletion in excess of 20 percent in each country. Australia fell in the middle of the distribution among the included markets for both first-party and third-party cookie deletion percentages.

To download the full report, The Impact of Cookie Deletion on Site-Server and Ad-Server Metrics in Australia: An Empirical comScore Study, please visit:

*Source: comScore

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