GA4 BigQuery Attribution refers to how traffic sources and conversion credit are assigned to user interactions and events within GA4’s BigQuery export.
Unlike the GA4 UI, where attribution is based on predefined models (e.g., last click or data-driven attribution), the GA4 BigQuery export provides raw event-level data that enables analysts to create custom attribution models using SQL queries.
GA4 BigQuery provides multiple traffic source fields, which represent different attribution scopes:
traffic_source (First-Touch Attribution)
The ‘traffic_source’ fields in BigQuery represent user-level first-touch attribution.
These fields capture the first campaign, source, and medium that brought the user to the website or app.
For example, if a user first visits your website via Google Ads, the traffic_source fields will always show google / cpc, even if the user returns later via different traffic sources (e.g., email, direct).
The ‘traffic_source’ fields are Ideal for analyzing long-term acquisition channels and identifying which campaigns drive new users.
session_traffic_source_last_click (Session-Level Last-Touch Attribution)
The ‘session_traffic_source_last_click’ fields represent last-touch attribution at the session level.
These fields capture the last non-direct traffic source that initiated the session.
For example, if a user first visits your website via Google Ads and later clicks an Email Newsletter link within the same session, the session is attributed to the Email Newsletter.
The ‘session_traffic_source_last_click’ fields are ideal for analyzing session-based reporting, such as sessions by traffic source or engaged sessions by traffic source.