Measurement · also called Incremental lift
Incrementality
Incrementality is the extra result, such as sales, installs or visits, caused by advertising that would not have happened without it, usually measured by comparing exposed and unexposed groups.
Attribution asks who was present when someone converted. Incrementality asks the harder question: would that person have converted anyway? Only the difference, the incremental part, was truly caused by the ad.
The cleanest way to measure it is an experiment. Split a comparable audience into a group that can see the ads and a holdout group that cannot; the difference in conversions is the incremental lift. Variants include geo experiments (turning ads on in some regions and off in others), ghost ads or intent-to-treat designs that identify who would have been shown an ad, and platform lift studies.
Incrementality often humbles marketers: retargeting and branded search can show great ROAS but low incremental value, because they reach people already about to buy. It is also a strong defence against attribution fraud, which steals credit for conversions that would have happened anyway. Tests need enough volume and time to be statistically meaningful, and results are often used to calibrate marketing mix modeling.
Think of it like this
Incrementality is like testing a new fertiliser by treating half the field and leaving the other half alone, then counting the difference at harvest.
An example
A retailer in Australia holds out 10% of its retargeting audience. The exposed group converts at 4.2% and the holdout at 3.8%, so only 0.4 points, about a tenth of attributed conversions, are incremental.
Related terms
Lift study
A lift study is an experiment measuring how much a campaign changed an outcome, such as awareness or sales, by comparing exposed people with a similar unexposed group.
Holdout group
A holdout group is a randomly chosen portion of an audience deliberately not shown a campaign's ads, used as a baseline to measure the ads' true incremental effect.
Attribution
Attribution is the process of assigning credit for a conversion, such as a sale, sign-up or install, to the ads, channels or touchpoints that a customer encountered beforehand.
Marketing mix modeling (MMM)
Marketing mix modeling (MMM) is a statistical method that estimates how much each marketing channel, plus factors like price and seasonality, contributed to sales, using aggregate historical data.
ROAS (return on ad spend)
ROAS (return on ad spend) is the revenue generated by advertising divided by the money spent on that advertising, usually shown as a ratio like 4:1 or 400%.
Sources: IAB guidelines