Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for outcome estimation and content item selection. In one aspect, a method includes training an outcome estimation model using both regression prediction quality measures and ranking prediction quality measures. In response to receiving a request for one or more content items; a predicted outcome is computed for each content item in a set of content items, each respective outcome being computed using the outcome estimation model and feature values associated with each respective the content item. Selection scores are computed for the content items using the predicted outcome. In turn, one or more content items are selected for presentation based on the selection scores; and data are provided that cause presentation of the one or more content items at a client device.