Attribution
Holdout Test
A controlled experiment where a portion of the target audience is deliberately excluded from seeing ads, creating a control group. By comparing conversion rates between the exposed group and the holdout group, you can measure the true incremental impact of your advertising. The most straightforward incrementality test to run. Requires enough volume to achieve statistical significance and a long enough test window (typically 2-4 weeks) to capture full purchase cycles.
Why it matters
It is the cleanest available answer to whether a channel is doing anything, because it observes the counterfactual directly instead of modelling it.
In practice
Hold out a randomly assigned share of the audience, run for a full purchase cycle plus the attribution window, and compare converted rates rather than platform-reported conversions.
Related terms