Programmatic
Unknown delta
The unknown delta is the share of programmatic ad spend that could not be traced or attributed to any identifiable fee or publisher payment in the 2020 ISBA/PwC supply chain study.
The unknown delta is the money that "went missing" in the most famous audit of programmatic fees. In 2020, the UK advertiser body ISBA and consultants PwC tried to follow individual impressions from advertiser to publisher, matching records from agencies, DSPs, SSPs and publishers.
They found that publishers received about 51% of advertiser spend on average and that roughly 15% of spend could not be attributed to any known participant. That untraceable portion was dubbed the "unknown delta". It was not necessarily stolen; it reflected data mismatches, timing, currency and undisclosed fees that nobody could reconcile. The study also struggled simply to match impressions end to end: only a small fraction could be fully traced.
The finding became shorthand for programmatic opacity and pushed the industry toward log-level data sharing, supply path optimization and standardised identifiers such as the supplyChain object. Later studies, including work by the ANA, continued to find significant fees and waste even when the unknown portion shrank.
Think of it like this
The unknown delta is like counting the cash at the start and end of a relay of cashiers and finding that part of it cannot be matched to any receipt.
An example
Out of every £100 in the ISBA/PwC sample, about £51 reached publishers, identified fees took about £35, and about £15 was the unknown delta.
Related terms
Ad tech tax
The ad tech tax is the combined share of an advertiser's spend taken by intermediaries, such as agencies, DSPs, data providers, verification vendors and SSPs, before the rest reaches the publisher.
Take rate
Take rate is the percentage of the money flowing through an ad tech platform that it keeps as its fee: platform revenue divided by the gross spend it handles.
Supply path optimization (SPO)
Supply path optimization (SPO) is a buyer's practice of choosing the most direct, cheapest and most trustworthy routes to the same inventory, and cutting unnecessary resellers and duplicate paths.
SupplyChain object (schain)
The SupplyChain object (schain) is a field in OpenRTB bid requests that lists, in order, every seller or intermediary that handled the impression on its way from the publisher to the buyer.
Discrepancy
A discrepancy is the difference between numbers reported by two systems for the same campaign, such as a publisher's and an advertiser's ad server counting different impressions or clicks.