Attribution is not the same as incrementality
An order can be attributed to an ad even when the shopper already knew the product or would have purchased through another path. Incrementality asks how much total demand and profit changed because the additional spend existed.
Choose a controlled comparison
- Select a stable SKU, campaign group, marketplace, or time window.
- Define the planned spend change and keep price, promotion, and listing edits limited.
- Record inventory, delivery promise, rating, competitor activity, and seasonality.
- Measure ad-attributed and total sales, units, and contribution profit.
- Use a comparison period or product group that is as similar as practical.
Calculate the incremental result
Estimate the change in total contribution before advertising, then subtract the change in ad spend. Review the result as a range because no simple observational test removes every outside influence.
Scale only the repeatable portion
Repeat the check across more than one period and watch what happens when spend returns to normal. Increase budgets where additional spend consistently creates incremental contribution within cash and inventory limits.