A method of selecting content items based on user interactions with provided content is performed at a server system. A subset of content items selected from a plurality of available content items is provided to a first user of the service. An amount of time that the subset of content items is provided to the first user is determined. Content item selection criteria for a second user of the service is adjusted based on the amount of time that the subset of content items is provided to the first user. In response to receiving a request for a content item from the second user, a content item is selected items for the second user from the plurality of available content according to the adjusted content item selection criteria. The selected content item is provided to the second user.