Incrementality
Incrementality measures the additional revenue ads generate vs. what would have happened without them, usually measured via holdout tests or geo-experiments.
What does Incrementality actually mean?
Incrementality is the share of attributed revenue that wouldn't have happened without the ads. Platform-reported ROAS includes conversions that would have occurred organically. Incrementality strips those out to find the true causal lift.
The canonical method: run a holdout test (random sample of users sees no ads) or a geo-experiment (some markets get ads, others don't) and compare conversion rates. The difference is incremental. Most performance teams find platform-reported ROAS is 30-60% inflated relative to incremental, meaning roughly half of attributed conversions would have happened anyway.
Incrementality testing is methodologically expensive (you give up some performance to learn) but informationally invaluable. Teams that don't test consistently over-allocate to bottom-funnel campaigns where attribution looks great but incrementality is low.
Example
A DTC brand runs a 4-week holdout test: 10% of US users see no Meta ads. The control group converts at 1.2%; the test group at 1.7%. Incremental conversion = 0.5 percentage points = ~30% of attributed performance. Reported ROAS of 4× translates to incremental ROAS of ~2.8×.
When it matters
Incrementality is the only honest measurement of paid social. Platforms over-attribute systematically; only experiments find the true number.
Related terms
Holdout test
A holdout test withholds ads from a randomly-selected control group, then compares performance vs. the test group to measure incremental lift.
Geo-experiment
A geo-experiment uses geographic regions as test/control groups, running ads in some markets and pausing in others to measure incremental lift.
MMM
MMM is a top-down statistical method that estimates each marketing channel's contribution to revenue using time-series data. It's privacy-friendly and attribution-window-agnostic.
View-through conversion
A view-through conversion is credited when a user sees an ad without clicking it, then converts within the attribution window.
Blended ROAS
Blended ROAS is total revenue divided by total ad spend across all channels. It's equivalent to MER, the honest top-down ad efficiency metric.
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