What is Incrementality?

Incrementality asks the only question that really matters: if this campaign had not run, would the sale still have happened? Attribution cannot answer it, because attribution assigns credit among ads that did run and never considers the counterfactual.

The channels most likely to be over-credited are the ones closest to the purchase. Retargeting reaches people already intending to buy. Branded search catches people typing your name. Both report beautifully and both, in part, are being paid for demand that already existed. That does not make them worthless — it makes their reported ROAS an overstatement of their value.

You do not need sophisticated tooling to learn something useful. A geo holdout, or simply pausing one campaign and watching total business revenue rather than that campaign’s own reporting, will tell you more than any attribution model. Run it long enough to clear your consideration cycle, avoid festive distortions, and accept that the answer will usually be less flattering than the dashboard. That is the point of asking.