Retargeting
Showing ads to people who already visited, browsed or abandoned - re-entering the conversation their behaviour started. Cheap and high-converting on paper, chronically over-credited in practice: many retargeted buyers were coming back anyway, so cap frequency and test incrementality. Remarketing is the same idea, historically via email lists.
Where it's used
Used for abandoned carts, site visitors and app reactivation. Good for gentle reminders. Measure it with a holdout, because it is easy to overrate.
How to calculate it
Extra conversions from ads = Conversion rate with ads - Conversion rate without ads
Worked example
Illustrative numbersCart abandoners are split at random. Of those who see ads, 9% buy. Of those who see none, 7% buy anyway.
Extra conversions
9 with ads - 7 without ads = 2 points
Share of sales the ads caused
2 points ÷ 9 with ads = 22%
What it tells you
The platform claims the whole 9%, but only about a fifth of those sales needed the ads. Work out the return from that part.