Attribution Model
A set of rules that determines how conversion credit is distributed across the touchpoints in a customer journey. Common models include first-touch, last-touch, linear, time-decay, and data-driven attribution.
Types of attribution models
Every conversion has a path — a sequence of interactions (ad clicks, organic searches, email opens, direct visits) that led to the final action. Attribution models define how to assign value across that path:
— First-touch assigns 100% of credit to the first interaction. Useful for measuring awareness channels, but ignores everything that happened after discovery.
— Last-touch assigns 100% to the final interaction before conversion. GA4 defaults to this for most reports. It overstates bottom-funnel channels like branded search and retargeting.
— Linear splits credit equally across all touchpoints. Simple and fair, but assumes every interaction has equal influence — which is rarely true.
— Time-decay gives more credit to touchpoints closer to conversion. Reasonable for short sales cycles, less useful for B2B journeys spanning weeks or months.
— Data-driven uses machine learning to calculate each touchpoint’s actual contribution based on conversion probability. Google removed all other models from GA4 in late 2023, making data-driven the default.
Why attribution needs complete data
Every attribution model — from the simplest last-touch to the most sophisticated data-driven — depends on seeing the full journey. When analytics data loss removes 40–87% of touchpoints, the model works on a fragment of reality.
Consider a customer who first discovers your brand through an organic search (blocked by an ad blocker), later clicks a display ad (tracked), and finally converts through a branded search (tracked). A last-touch model credits branded search. A data-driven model credits display. Neither knows the organic visit existed. The channel that actually introduced the customer gets zero credit — and zero budget in the next planning cycle.
Multi-touch attribution only works when you can see all the touches. Cookieless analytics ensures no touchpoint is invisible, giving any attribution model the complete input it needs.
Attribution model comparison
| Model | Credit Distribution | Best For |
|---|---|---|
| First-touch | 100% to first interaction | Awareness measurement |
| Last-touch | 100% to last interaction | Direct-response campaigns |
| Linear | Equal across all touchpoints | Long, multi-channel journeys |
| Time-decay | Weighted toward conversion | Short sales cycles |
| Data-driven | ML-calculated per touchpoint | High-volume, complete data |
Note: GA4 deprecated all models except data-driven and last-click in November 2023. Data-driven attribution requires sufficient conversion volume and — critically — complete data to produce reliable results.