Data-driven attribution (DDA) is Google Ads' default attribution model. It uses a machine learning model to estimate each touchpoint's contribution to conversion across multi-touch journeys. Unlike last-click or first-click, it measures actual incremental value.
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Difference from last-click: last-click counts only the final click; first impression, view-through, and mid-journey touches receive zero credit. DDA measures these touches at scale; a user who saw a YouTube ad, then clicked through Search, then came back via Display retargeting has the conversion attributed proportionally across all three touchpoints.
Conditions that make DDA work well: sufficient conversion volume (30+ conversions per campaign in 30 days), a conversion window aligned with the purchase cycle, and clean GA4 + Google Ads data flow.