IAB and IAB Europe define incrementality, grade test methods by causal strength
Attribution distributes credit among the touchpoints a customer saw before buying. Incrementality asks whether removing one touchpoint would have removed the purchase itself, a distinction the IAB and IAB Europe formalized in a joint paper on November 3, 2025. The paper grades four families of measurement methods by causal strength: experiment-based tests such as randomized control trials, holdouts, ghost ads and matched markets rate strong though narrow in scope; model-based counterfactuals such as synthetic control and propensity models rate strong to moderate; econometric approaches such as marketing mix modeling rate moderate to weak with high scope; and hybrid proxies, including new-to-brand percentages and platform-reported incrementality, rate as the weakest tier. The task force that produced the grading included staff from Criteo, Meta, Instacart, Walmart, Uber and Google.
Budget arguments now lean on these grades directly. Research cited around Smartly's March 2026 agreement to acquire INCRMNTAL found that 67.4% of marketers rank proving incremental return as their top measurement priority, ahead of cross-channel attribution accuracy at 55.1%. Confidence has not kept pace: IAB's State of Data 2026 report, published February 7, 2026, recorded up to 75% of buy-side decision-makers rating attribution, incrementality tests and mix models as underperforming. Media buyers relying on platform-reported lift numbers should treat them as the weakest tier of evidence in the IAB's own framework, and weigh a geo experiment or holdout test before shifting budget on a vendor's self-reported figure.