Lift test
A lift test is a randomized test that holds some people back from the ads, and it measures incrementality.
A platform's own count has no held-back group, so it counts sales from people who would have bought anyway. Researchers compared 663 randomized experiments at Facebook with two methods that estimate effects without a test. For lower-funnel outcomes, the experiments' median lift was 5%, while the other two methods put it at 24% and 64%.
Incrementality is what a lift test measures, and a media mix model is calibrated with lift tests. Each platform makes its counts its own way, so a move between channels needs a lift test or a media mix model.
Example
With lift test results, a shift between tactics inside one channel is judged against a lift-adjusted target, the platform target corrected by those results. That matters most in retargeting and brand search, where the platform's own return on ad spend overstates what ads caused by the widest margin.