document: Dynamic cost-per-action mechanisms and applications to online advertising We study the Cost-Per-Action or Cost-Per-Acquisition ( CPA ) charging scheme in online advertising . In this scheme , instead of paying per click , the advertisers pay only when a user takes a specific action ( e.g. fills out a form ) or completes a transaction on their websites . We focus on designing efficient and incentive compatible mechanisms that use this charging scheme . We describe a mechanism based on a sampling-based learning algorithm that under suitable assumptions is asymptotically individually rational , asymptotically Bayesian incentive compatible and asymptotically ex-ante efficient . In particular , we demonstrate our mechanism for the case where the utility functions of the advertisers are independent and identically-distributed random variables as well as the case where they evolve like independent reflected Brownian motions .
doc_bio_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O