Selecting Content Based on Performance of a Content Slot

In one aspect, a method includes receiving a request for content to be presented in a specified content slot of a specified content page; calculating an active view scroll distance of the specified content slot with respect to the specified content page, the active view scroll distance corresponding to a measurement of a distance that the specified content page would have to be scrolled to change visibility of content displayed in the specified content slot by a specified amount; performing an auction of content items utilizing in part the active view scroll distance; and providing one or more content items in response to the request and as a result of the auction.