Incrementality
Incrementality is the share of conversions that advertising actually caused — conversions that would not have happened without the ads, as opposed to conversions the ads merely touched.
Attribution asks "which ad touched this conversion?"; incrementality asks "what would have happened anyway?" The gap between them is largest exactly where reported performance looks best: brand search, retargeting, and any campaign harvesting people who had already decided.
The workable tests do not require a data team: geo holdouts (turn a channel off in matched regions), audience holdouts, and pause-tests on suspiciously efficient campaigns. Run them when a budget line becomes big enough that being wrong about it matters.
Knowing what Incrementality means isn’t the edge.
Knowing what it’s doing to live accounts right now is. Operator notes from $200M+ in managed spend — sent when we find something worth your time.
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