The study addresses the key sources of discrepancy between server-based and panel-based data in Australia and reveals that cookie deletion can lead to large overstatements in servers’ measurement of the size of online audiences. Without appropriate adjustments, site server audience reports can be inflated up to 2.7 times the actual number of unique visitors.

Topics covered in the report include:

• Thorough discussion of the study’s methodology.
• Quantification of the degree to which cookie deletion leads to an overstatement in site-servers’ estimates of the number of unique site visitors.
• Comparison of first-party vs. third-party cookie deletion rates and the resulting overstatement in servers’ estimates of the size of site audiences and the reach of online advertising campaigns.
• A comparative look at cookie deletion rates across select global markets.
• Implications for the industry and comScore’s proposed solution for accurate audience measurement.