Measurement & Tracking
Attribution Model
An attribution model is the rule set that decides how credit for a conversion is divided among the ad interactions that preceded it, such as last click, first click, or data-driven.
In practice
A customer clicks a YouTube ad, then a Shopping ad, then a brand search ad, then buys. Which ad gets the sale? Last click gives it all to the brand search. First click gives it all to YouTube. Data-driven attribution splits it based on the observed contribution of each step. The model changes nothing about what happened; it changes what the reports say and, under Smart Bidding, what the algorithm learns from.
Google Ads defaults to data-driven for most conversion actions and has retired the position-based and time-decay models. GA4 has its own model settings, which is one reason GA4 and Google Ads numbers rarely agree.
The practical implications: never compare campaigns across accounts or platforms without checking their models, expect brand campaigns to look worse and upper-funnel campaigns to look better when you move from last click to data-driven, and make the switch deliberately with a note in the change log.
Why it matters
It decides which campaigns look good, and under automated bidding, which ones get budget.
RELATED TERMS
Data-Driven Attribution (DDA)
Data-driven attribution is Google's model that assigns conversion credit across ad interactions using machine learning on your account's actual conversion paths, rather than a fixed rule like last click.
MER (Marketing Efficiency Ratio)
Marketing efficiency ratio is total business revenue divided by total marketing spend across all channels, measured without platform attribution.
GA4 Key Events
Key events are the events in Google Analytics 4 that you mark as important business outcomes; they replaced the term conversions in GA4 and can be imported into Google Ads as conversion actions.
Written by Ilya Bulychev, Founder, Live PPC Ads. Part of the PPC Glossary.
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