What is incrementality in marketing?

Incrementality measures the conversions that happened only because of a marketing activity, that would not have happened otherwise. It is the difference between the sales you got with an ad running and the sales you would have got without it.

Why it matters

Attribution can credit a channel for sales it did not truly cause. The classic example is branded search or retargeting taking credit for customers who were always going to buy. Those conversions are attributed, but not incremental. Cutting the campaign would not lose them. Incrementality testing exposes that gap.

How it is measured

The gold standard is a controlled experiment: hold out a random group from seeing an ad and compare their conversion rate to the exposed group. The difference is the incremental lift. Geo-based holdouts and conversion-lift studies are common practical versions.

Where it fits

Incrementality is the validation layer on top of attribution and modeling. Attribution and MMM tell you what to do day to day; incrementality tests confirm the channels are genuinely driving growth rather than claiming credit. Complete attribution data, like the first-party measurement Trakt provides, makes those tests cleaner because the baseline conversions are counted properly to begin with.