Incrementality

Attribution asks "which ad gets credit for this sale?" Incrementality asks "would this sale have happened without any ad?" The gap matters most for brand search, retargeting and existing customers, where platforms often report strong results for people already on their way to buy. The only reliable way to measure it is an experiment: a group that sees ads compared with a similar group that doesn't.

Where you'll see it

In Google Ads, lift studies are under Goals > Measurement > Lift measurement for eligible accounts, and geo-based experiments can run with Google's support or open-source tools. In Meta Ads Manager, use Experiments to set up a Conversion Lift test. TikTok offers Conversion Lift Studies through its account teams. Incrementality is a study you run, not a column you read.

A geo test paused the campaign in matched regions, and total conversions there fell by only 20%: 300 × 20% = 60. Both numbers are "correct", but only one tells you what the spend actually bought.