Incrementality
Incrementality measures how much of a campaign’s results would not have happened without it: the sales, visits or conversions that advertising genuinely adds.
Many of the conversions a campaign claims would have happened anyway. Someone who was already going to buy sees a retargeting ad, buys, and the ad takes the credit. To separate what advertising causes from what it merely accompanies, an exposed group is compared with a similar control group that did not see the campaign, either because it was deliberately held out or because it lives in an area with no spend. The difference between the two is the incremental effect.
It is the question any finance director ends up asking, and it carries more weight as budgets come under closer scrutiny. There are variants depending on what is measured: conversion lift for online sales, incremental visit studies for drive to store, geographic experiments when people cannot be split. It takes patience and volume. A test with little data produces results that look precise and are not.
