Privacy-first web advertising: a measurement update

In January, we shared how Google’s advertising teams have been evaluating the proposals in Chrome’s Privacy Sandbox, an open-source initiative to replace third-party cookies with viable privacy-first alternatives that can support the publishers and advertisers who help keep the web open and accessible.

Today, we’re going to explain how the latest proposals in the Privacy Sandbox can solve for key conversion measurement use cases on the web while preserving privacy – and we’ll also share a new resource to help you learn more about the overall initiative.

Conversion measurement

Chrome’s conversion measurement proposals center around an API that would have the capability to report both event-level and aggregated information. Event-level information is helpful when businesses need data to be more granular, such as deciding how much to bid on impressions or modeling conversions. Aggregated information is important for summarizing campaign performance, like reporting total conversion value or return on investment.

To make sure that the API preserves privacy, and that any data reported can’t be used to track individual people as they move across the web, the API uses one or more of the following techniques:

• Aggregate the data that is reported so that each person’s browsing activity and identity remain anonymous among a large group of conversions.
  
• Limit the amount of information reported about each conversion, so it’s not possible to expose the identity of the person behind the conversion.
  
• Add "noise" to the data reported, which protects an individual’s privacy by including some random data along with the actual conversion results.

The Chrome team recently shared new proposals for how the API could apply these privacy considerations while reporting view-through conversions and cross-device conversions:

For view-through conversion measurement, Chrome proposes that advertisers use the event-level capability of the API to get a report on the conversions that happen on their website and are attributed to ad views across the web. The browser would enable this by registering the ad impressions that take place across websites and then matching any conversions that happen on an advertiser’s website back to the initial views. To prevent any conversion data from being used to track people individually, the Chrome API would limit the amount of information shared about each conversion and add noise to the data. 

Then, when advertisers are interested in reporting on the total number of view-through conversions, for a video ad campaign as an example, Chrome proposes that they can use the API’s aggregate reporting capability. This would allow advertisers to get more precise information on key metrics for the overall campaign without compromising people’s privacy. That’s because aggregate reporting keeps people’s identities and their browsing histories anonymous as it only shares data across a large group of conversions.

For cross-device conversion measurement, Chrome proposes that advertisers use the API’s event-level capability to report on the conversions that happen on their website and are attributed to ad views or clicks that happen on another device. This would only be possible if the people converting are signed into their browser across their devices. Access to this capability would enable cross-device measurement for all participating ad providers and networks.

The proposals in the Privacy Sandbox will change how measurement works for digital ads, but are designed to support key measurement use cases while protecting people’s privacy. We’re beginning to run simulations to understand how different use cases might be impacted by the privacy considerations made in Chrome’s various proposals and we look forward to sharing our findings in the near future.

Resources

We know that there are many questions about the Privacy Sandbox and that there is broad interest in learning more about each of the proposals. The Chrome team recently built a new website, privacysandbox.com, with an overview of this effort, FAQs, and links to additional resources. We’ll also continue to share regular updates about our work across Google’s ads teams to adopt the Privacy Sandbox technologies for our web advertising and measurement products.