Google tests the ad performance of third-party cookie replacements

Chrome is currently set to phase out third-party cookies in 2024, and Google has been working on privacy-preserving alternatives for ads and publishers. Google Ads today shared the results of an experiment comparing the existing system to the upcoming replacement.

We created two experiment arms on a share of Chrome traffic. On one arm, we continued using third-party cookies. On the other, we replaced third-party cookies with a combination of privacy preserving signals for IBA solutions while maintaining the use of third-party cookies for other use cases such as measurement and remarketing.  

This took place in the first quarter of 2023 to measure the performance of interest-based audience (IBA) solutions “when they rely on a combination of privacy-preserving signals,” like contextual information, the Privacy Sandbox Topics API, and first-party identifiers such as Publisher Provided IDs.

Highlights from Google Ads and Display & Video 360 include:

• “The experiment showed that when using interest-based audience (IBA) solutions with privacy-preserving signals on the display network, Google Display Ads advertiser spending on IBA — as a proxy for scale reached — decreased by 2-7% compared to third-party-cookie-based results.”
• “For conversions per dollar, as a proxy for return on investment, the decrease was 1-3%.”
• “Finally, we also observed that click-through rates remained within 90% of the status quo.”

Google’s overall conclusion is that the alternatives “showed promise compared to third-party cookies,” but:

These results – while encouraging – should not be considered as an unequivocal indicator of Google’s IBA performance after the third-party cookie deprecation. The current experiment measures the effectiveness of serving interest-based audiences; the results of future experiments including measurement, remarketing, and other use cases may vary.

Google also found that campaigns using AI-powered optimizations were “less impacted by the removal of third-party cookies, indicating that machine learning can play a significant role in driving results.”

The company is planning more rounds of testing.