What is the unknown delta in programmatic advertising?
The unknown delta is the portion of programmatic ad spend that cannot be traced to either a known fee or a publisher payment. The term comes from the 2020 ISBA and PwC UK study, which could only match a fraction of impressions end to end and found roughly 15% of advertiser spend unattributable. It symbolizes the opacity of the supply chain.
ISBA and PwC traced impressions from advertisers to publishers using data from agencies, DSPs, SSPs and publishers. On matched impressions, publishers received about 51% of spend; identifiable fees took about 35%; the remaining ~15% was the unknown delta. Much of the problem was simply that data could not be matched across companies.
Follow-up studies by ISBA and others found improved matching when participants shared log-level data. The concept pushed buyers toward supply path optimization, log-level transparency clauses and fewer intermediaries, and fed into debates about the ad tech tax.