Attribution
Also known as: Marketing attribution, Conversion attribution
In short
The process of assigning credit for a conversion or its value to eligible marketing interactions according to a defined model and measurement scope.
Decide which interactions receive credit
Attribution connects recorded outcomes with eligible interactions before them. A model determines whether one touchpoint receives the credit or several touchpoints share it.
The model is only part of the definition. Channel coverage, identity matching and the lookback period also affect the result. In Google Analytics, user-scoped, session-scoped and event-scoped traffic dimensions answer different questions, so their attribution behavior is not identical.
A first-user source describes acquisition of the user. A session source describes the visit. An attributed key event concerns credit for the outcome. Reading these as the same measure creates misleading comparisons.
Illustrative allocation
Imagine a fictional shopper discovering a store through organic search, returning through a paid ad and purchasing later. A model that credits the last eligible paid interaction could assign the purchase to that ad. A model using multiple touchpoints could distribute credit differently.
The underlying order remains the same. A reporting change moves credit; it does not change the transaction that occurred.
Do not confuse credit with added demand
An attributed sale may have happened without the ad. Attribution alone cannot answer that counterfactual question. Use an appropriate controlled experiment to evaluate incrementality. When comparing reports, align outcomes and dates, then inspect model settings and eligible channels before deciding that one system is wrong.