Abstract: This specification describes technologies relating to displaying online content. In general, one aspect of the subject matter described in this specification can be embodied in methods that include receiving a collection of advertisement candidates for display in an online medium, the advertisement candidates each assigned a quality score calculated based at least in part on a measure indicative of relevance of the respective advertisement candidate to online content for concurrent display in the online medium, determining a score threshold based at least in part on relationships among multiple quality scores of the quality scores associated with the advertisement candidates in the collection of advertisement candidates, and based on the determined score threshold, identifying a subset of advertisement candidates of the collection for display. Other embodiments of this aspect include corresponding systems, apparatus, and computer program products.

Abstract: In general, in one aspect, a first request to provide one or more advertisements on a first web page is received, the first web page comprising one or more items of web content related to a query. A first quality score is calculated for a first advertisement included in a set of one or more candidate advertisements. The first advertisement is presented on the first web page based at least in part on the first quality score. A second request is received to provide one or more advertisements on a second web page, the second web page comprising one or more different items of web content related to the query. A second quality score for the first advertisement is calculated based at least in part on the previous presentation of the first advertisement. It is determined whether to present the first advertisement on the second web page based at least in part on the second quality score.