Holdout Testing
By the AdFlint research team · Last reviewed July 2026
Permanently excludes a randomly selected share of your audience from seeing ads, so their behavior serves as an ongoing baseline.
A fixed percentage of users or accounts is suppressed from targeting for the duration of the test, and the gap between held-out and exposed groups gives you the incremental effect. Advertisers keep a standing holdout on retargeting and CRM audiences, where reported returns are most likely to be double-counted demand. Watch for leakage: if the held-out group can still be reached by other campaigns, the baseline is contaminated.
Holdout Testing compared with
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