Abstract: An example process includes: obtaining information about call-outs from at least one bidder of an online content auction, where the information spans a time period and the information identifies which call-outs, within the time period, did not result in a response; identifying, based on the information, one or more features that are common to call-outs that did not result in at least a threshold number of responses from the at least one bidder; generating a model for the at least one bidder that predicts whether the at least one bidder will respond to a call-out associated with the one or more features; using the model to determine a percentage of additional call-outs having the one or more features to send to the at least one bidder; and sending the percentage of additional call-outs to the at least one bidder.