Ads Manager reports conversions that happened after someone saw or clicked an ad. Some of those people would have bought anyway. Incrementality is the part that wouldn't have happened without the ad.
How it's measured
- Conversion lift test: Meta splits people into a group that can see your ads and a holdout that can't, then compares results.
- Geo test: turn ads off (or up) in some regions and compare them with similar regions.
- MMM: a statistical model that estimates each channel's contribution from spend and sales over time.
Why it matters
Platform-reported ROAS can over-credit some ads, like retargeting and sale statics that catch people already on their way to buying, and under-credit the videos that created the demand. Run lift tests when the stakes are high, and check MER to keep platform numbers honest.
More: How Meta attribution works.
Related: attribution window, ROAS.
