Chrome has recently added instrumentation to measure how many attribution reports are removed by browsing data removal in Chrome.
With cookie-based measurement, data deletion after a conversion happens isn't an issue as the ad-tech learns about the attribution immediately at conversion time.
The delayed reporting mechanism in the API means reports are kept on device for longer periods of time and thus are more susceptible to browsing data removal.
In the current Origin Trial for Attribution Reporting we observe:
Some, but not all, sources that get deleted are also associated with reports that get deleted. If a source is deleted before the conversion is ever registered, the total loss of reports can be greater than 6.5% when comparing API reports to cookie-based reports. Note that these numbers cover all reports generated by Chrome, and may vary across reporting origins.
You should expect to see differences when comparing API reports and cookie-based reports for these reasons. You may want to divide these into "explained" and "unexplained" gaps using the numbers above.
We have also previously posted numbers for report loss due to network-related errors here.
Happy to clarify any of the above!
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What would user actions on Chrome lead to their deletions?
IIRC, Chrome stores the attribution data in a DB file under the user's profile folder. Therefore, the deletion of attribution data would happen when the user removes their profile in Chrome.
Are there others?
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