Incrementality
Also: Incremental lift · Lift test · Geo holdout
Incrementality is the number of conversions that happened because of an ad campaign and would not have happened without it. It is measured with controlled experiments — holdout groups or geo tests — rather than with attribution.
Attribution answers "which ad touched this user"; incrementality answers "did the ad change anything". The two diverge most on brand keywords, retargeting, and view-through conversions, where attributed conversions are often largely non-incremental.
The practical method is a geo holdout: pause spend in comparable regions and compare their conversion trend to regions where spend continued. It is slow and costs budget, and it is the only way to know a channel's real multiplier.
Related terms
In Roasy
Roasy computes this across every ad network, Adjust, and RevenueCat on one screen — real revenue, cohort windows, and the same definition everywhere.