User actions responsive to a plurality of web pages are tracked and included in records in a data store. A conversion score is calculated for each traffic source of a plurality of traffic sources, the conversion score based at least in part on the tracked user actions. A traffic source quality score is calculated for each of the plurality of traffic sources, and the plurality of traffic sources are ranked based at least in part on the traffic source quality scores. The traffic sources are allocated to sets based at least in part on the ranking.