@dmarti and I are back with more publisher use cases for the Privacy Sandbox, this time focused on reporting needs. https://github.com/dmarti/in-browser-auction-publisher-issues/edit/main/reporting.md. We focused heavily on impression reporting in this document because conversion reporting has been well covered on the advertiser side 1/

The reason impression reporting might be an issue in the future world is that some of the "bird" proposals, like TURTLEDOVE, decouple ad serving (in some cases) from the publisher ad server. The ad serves to the user, but the publisher has no idea it happened! 2/

Reporting becomes available, but it is a) delayed; b) aggregated; and c) has noise added. This raises a number of potential issues that are hard to wrap your head around. Delays, aggregation and noise are critical for increasing privacy, and can be acceptable for... 3/

conversion measurement purposes, but for publisher impression reporting, are potentially quite painful. Some key issues we identify are: 1) publishers need to know EXACTLY how much money they're making!; 2) Publishers need to be able to deploy changes... 4/

to their site and gather near real-time impression data to detect potential issues; 3) publishers need to be able to a/b test different code to find revenue differentials that are very small and can't accept noise; and 4) publishers need to be able to prove to advertisers... 5/

and other interested parties that certain ads were served or not served (in the case of ads that would be against the publisher's brand guidelines). Some elements of the proposed reporting APIs in the Privacy Sandbox might be extended to accommodate for these issues, 6/

some of the bird proposals would solve some of these use cases, or possibly publishers could have impression data pushed directly and immediately to their ad server (since that has no cross-site utility, perhaps), but these use cases definitely need to be addressed. 7/

We're presenting these in the W3C in the next week or two and appreciate feedback from the industry on what we've put together and potential solutions! 8/8