The Interactive Advertising Bureau on October 20, 2026 released a draft Cross-Channel Measurement Decision Guide for public comment, a document meant to help marketers decide what to do when marketing mix models, incrementality tests and attribution give different answers about the same campaign. Comments close on November 4, 2026.

In Short

Advertisers use several different ways to work out whether their ads worked, and those methods often disagree with each other. The IAB, the main US trade body for digital advertising, has written a draft guide that starts from the business decision being made and works back to which kind of evidence fits it best. Anyone can comment on the draft until November 4, 2026, after which the IAB says it will finalize it, though it has not said when.

What the IAB published

According to the IAB, the guide was developed as part of Project Eidos, the trade body's measurement modernization program. The announcement, datelined New York, describes the release as advancing the IAB's work "to help marketers use cross-channel measurement evidence to make better-informed investment and optimization decisions."

The intended audience is spelled out: marketers, agency teams and measurement partners. The subject matter is equally specific. According to the IAB, the guide offers "a decision-first approach to selecting, interpreting, and applying evidence from methods like Marketing Mix Modeling (MMM), incrementality testing, and attribution, including when their findings appear to tell conflicting stories."

That last clause is the core of the document. Any advertiser running more than one measurement method has encountered the problem. A marketing mix modelling exercise, which estimates the contribution of each channel from aggregate spend and sales data over time, can credit a channel with one return. A platform's attribution report can credit it with another. A controlled test of incrementality, which compares exposed and unexposed groups to isolate the sales a campaign actually caused, can produce a third figure that matches neither.

The IAB's answer is to change the starting point. According to the announcement, "Rather than starting with whatever metrics happen to be available, it starts with the business decision at hand and works backward to the evidence best suited to inform it."

Three connected parts

The guide has three components, according to the IAB.

The first is the Decision Guide itself. It lays out a sequence that runs from business outcome to decision, then to measurement question, measurement approach, evidence, interpretation and, finally, action. Seven steps, in a fixed order.

The second is the Decision Navigator. This applies the sequence to common decisions. The IAB names two examples: allocating budget across channels, and assessing whether an investment is creating incremental value. According to the announcement, the Navigator "helps readers determine which methods fit the question and how to weigh the evidence."

The third is the Measurement Reference Library. Rather than writing new definitions, this section "brings together existing metric definitions and supporting context," according to the IAB, so that readers can interpret the evidence used in the other two parts.

That design choice matters. The library collects definitions that already exist; the announcement does not describe it as setting any new metric standard. The guide, as presented, is an interpretive framework rather than a measurement specification, and it does not tell anyone how to count an impression, define reach, or deduplicate audiences across platforms.

What the IAB said

David Cohen, chief executive of the IAB, framed the problem in terms of trust. "Measurement only works if the industry trusts the answers it produces, and right now, MMM, incrementality, and attribution can each tell a different story about the same campaign," Cohen said. "This guide doesn't ask marketers to pick a winner among those methods. It gives them a disciplined way to work through the question at hand and make a decision they can stand behind. That's exactly the kind of foundational work Project Eidos was built to do."

The phrase "doesn't ask marketers to pick a winner" is a notable position for a trade association whose membership includes sellers of each of those methods. MMM vendors, platforms that report attributed conversions and companies that sell lift studies all have commercial reasons to see their own numbers treated as the authoritative one.

Matt Shapo, senior director of measurement at the IAB, gave the most concrete example in the announcement. "We built this to be used, not just read," Shapo said. "The real test is whether it holds up in an actual planning conversation, like when a channel reports a strong attributed ROAS that an incrementality test doesn't back up. That's exactly the kind of scenario we want the industry weighing in on before we finalize it."

That scenario - high ROAS under attribution, weak results under a holdout test - is the most familiar version of the conflict. Attribution models credit sales to ads that preceded them, whether or not the ads caused those sales. Incrementality tests try to measure only the sales that would not have happened otherwise. For channels that reach people already likely to buy, such as branded search or retargeting, the gap between the two can be wide.

Cohen returned with a second statement built on survey data. "Marketers rely on measurement to make consequential investment decisions, but they don't always feel confident that their approaches deliver the evidence they need," he said. "60-75% say advanced measurement falls short across key dimensions such as rigor, timeliness, trust, and efficiency, and this guide helps them connect evidence from different measurement approaches to the decision at hand, understand what the findings can support, and identify where additional testing or calibration is needed. That gives brands and their partners a stronger foundation for putting measurement into action."

The 60-75% figure is hyperlinked in the IAB page to the trade body's 2026 State of Data report. The release does not restate the survey's sample or method. PPC Land's coverage of that report, published in February, recorded that it surveyed more than 400 senior planning and analytics decision-makers at US brands and agencies, with 60% to 75% rating their current approaches poorly across critical dimensions. The same report found that no media channel was fully represented in marketing mix models and that buyers expected to expand incrementality testing from three to five tests per year to 11 or more.

What the IAB wants to hear

The IAB lists three areas where it is "especially seeking feedback":

  • whether the guide reflects real-world measurement decisions;
  • whether its method-fit and interpretation guidance holds up when results conflict;
  • whether its scenarios are realistic enough for day-to-day planning.

All three are practical questions. None asks for comment on metric definitions, technical specifications or certification criteria, which is consistent with the guide's interpretive rather than standard-setting role.

The comment window

According to the IAB, "The public comment period is open from October 20, 2026 through November 4, 2026." The announcement directs readers to review the guide and submit feedback through a single link. That link points to an IAB guidelines page whose address describes it as a "cross-channel measurement guide open for 15-day public comment period."

Fifteen days is shorter than other recent IAB consultations. When the trade body released its Redefining Media Types Standard in July, it gave the industry 30 days to comment, until August 8, 2026. Campaign Data Standards 1.0, the first Project Eidos output, opened for comment on May 14, 2026, with a closing date that PPC Land found cited as both June 10 and June 14 in the IAB's own materials, and a final version expected in the fourth quarter of 2026.

A small inconsistency also appears in the announcement's naming. The page headline calls the document a "New Guide to Inform Cross-Channel Measurement Decisions." The body text calls it the "Cross-Channel Measurement Decision Guide." The page address uses "cross-channel-measurement-decisions." All three refer to the same release.

Where it sits in Project Eidos

The IAB first presented Project Eidos in early 2026 as an industry-wide initiative built on shared principles, standards and frameworks. PPC Land's August coverage dated the program's announcement to February 2, 2026, and placed the AI visibility measurement framework released on August 3 within it.

The new guide extends that sequence. Campaign Data Standards 1.0 dealt with how campaign data is labeled so that platforms classify the same elements the same way. The AI visibility framework set a vocabulary for measuring brand presence in AI-generated answers. The cross-channel guide moves one step further downstream, to the point where a planner has the numbers and has to decide what they mean.

The IAB page also points to a related release. Its "Related Content" panel and "previous chapter" link both reference "IAB Releases Measurement Services Addendum v1.0 for Public Comment," a separate document the announcement does not describe.

Earlier IAB work on the same methods

The trade body has addressed parts of this problem before. In November 2025, the IAB and IAB Europe published guidelines for incremental measurement in commerce media, which grouped methods into four types by causal strength and recommended econometrics, including MMM, as the primary approach for cross-channel budget allocation. Those guidelines also listed MMM's limits: backward-looking analysis, low granularity and multicollinearity.

The Media Rating Council, working with the IAB, finalized attention measurement guidelines in November 2025 after a draft in May and a comment period through July. The MRC is not mentioned anywhere in the new announcement.

Outside the trade body, the tools the guide addresses have spread quickly. Google made its open-source Meridian model globally available in January 2025 with more than 20 certified partners. IAB Australia published a landscape of 12 MMM vendors in September 2025. PPC Land has also examined the incentives at play when a platform builds the MMM that measures its own channels, using Meta's Robyn as the case. A neutral, method-agnostic guide from a trade body arrives into a market where several of the most widely used models are built and distributed by the largest sellers of advertising.

Why this matters for advertisers

Budgets are moving on this evidence. The IAB's September revision of its US ad spend outlook, to 12.3% growth for 2026, came with a finding that 86% of buyers expect AI to change media measurement within a year. When MMM, attribution and lift tests point in different directions, the practical result is that the same campaign can be expanded by one team and cut by another, depending on which report reaches the meeting first.

A decision-first framework does not resolve which method is correct. What it can do, if the final version matches the draft's description, is give buyers, agencies and sellers a shared sequence for the argument: what decision is being made, what question that decision needs answered, and which evidence can actually answer it. For sellers whose channels look strong in attribution and weaker in holdout tests, that sequence could carry consequences. For buyers, it offers a reference point that does not come from any one vendor.

Whether the guide gains traction will depend on adoption. The IAB has not said that it plans any certification, compliance program or audit tied to the document, and nothing in the announcement suggests one.

What the announcement leaves out

The IAB page does not state:

  • Authorship. No working group, committee, task force or participating companies are named. Only the IAB's Cohen and Shapo are quoted.
  • Length and format. The number of pages, decisions or scenarios in the Decision Navigator is not given, nor is the format of the Measurement Reference Library.
  • Channels and metrics. Apart from ROAS in Shapo's example, no specific metrics are named. The page does not say which channels the scenarios cover, or whether the guide addresses impressions, reach, frequency, deduplication, attention or outcome metrics.
  • Finalization date. The IAB says it will finalize the guide after comments, but gives no target date.
  • How comments are handled. The page does not say whether submissions will be published, how they will be reviewed, or whether a revised draft will be recirculated.
  • Role of other bodies. Neither the IAB Tech Lab nor the Media Rating Council is mentioned in connection with the guide, and there is no reference to accreditation or certification.
  • Access. The page does not say whether the final guide will be free or restricted to IAB members.
  • Survey method. The 60-75% statistic is linked to the State of Data report but its sample and fieldwork dates are not restated in the release.

Timeline

Summary

Who: The Interactive Advertising Bureau (IAB), with statements from chief executive David Cohen and senior director of measurement Matt Shapo. The guide is aimed at marketers, agency teams and measurement partners.

What: A draft Cross-Channel Measurement Decision Guide, released for public comment as part of Project Eidos. It has three parts - the Decision Guide, the Decision Navigator and the Measurement Reference Library - and sets out a decision-first approach to interpreting evidence from marketing mix modeling, incrementality testing and attribution, including when those methods conflict.

When: Released on October 20, 2026. The public comment period runs from October 20, 2026 through November 4, 2026. No date for the final version has been given.

Where: Announced from New York, with the draft and the feedback form hosted on the IAB website.

Why: According to the IAB, 60-75% of marketers say advanced measurement falls short on rigor, timeliness, trust and efficiency, and MMM, incrementality and attribution can each tell a different story about the same campaign. The guide aims to give buyers and sellers a shared sequence for deciding which evidence fits which decision, without declaring any single method the winner.