Incrementality testing measures the additional conversions a marketing activity actually caused, as opposed to conversions that would have happened anyway. It typically compares an exposed group against a control group that was withheld. It answers the question attribution cannot: did this spend create demand or just take credit for it?

Attribution tells you what a channel gets credit for. Incrementality tells you what would have happened if you had not run it at all, which is the question that actually matters for budget. Branded search is the classic case: it looks superb in every report, and much of it would have converted anyway. Incrementality is how you find out.

Example:

Pausing a channel in one region while leaving it running elsewhere shows whether conversions actually drop, which reveals how much the channel truly caused.

How is incrementality different from attribution?

Attribution assigns credit for conversions that happened. Incrementality measures whether those conversions would have happened anyway without the spend.

Why does incrementality matter for budget decisions?

A channel can take credit for demand it did not create. Incrementality reveals genuine causation, so budget goes to spend that actually produces additional revenue.