In this paper we design information elicitation mechanisms for Bayesian auctions. While in Bayesian mechanism design the distributions of the players' private types are often assumed to be common knowledge, information elicitation considers the situation where the players know the distributions better than the decision maker. To weaken the information assumption in Bayesian auctions, we consider an information structure where the knowledge about the distributions is arbitrarily scattered among the players. In such an unstructured information setting, we design mechanisms for unit-demand auctions and additive auctions that aggregate the players' knowledge, generating revenue that are constant approximations to the optimal Bayesian mechanisms with a common prior. Our mechanisms are 2-step dominant-strategy truthful and the revenue increases gracefully with the amount of knowledge the players collectively have.Extensions of our results. In our main results, the seller asks the players to report the distributions in their entirety, without being concerned with the communication complexity for doing so. This is common in information elicitation and allows us to focus on the main difficulties in aggregating the players' knowledge. In Appendix D, we show how to modify our mechanisms so that the players only report a small amount of information about the distributions.Furthermore, in the main body of this paper we consider auction settings where a player i's knowledge about another player i ′ for an item j is exactly the prior distribution D i ′ j . This simplifies the description of the knowledge graphs. In Appendix E, we consider settings where a player may observe private signals about other players and can further refine the prior.Future directions. As Bayesian auctions require the seller (and the players under common-prior assumption) has correct knowledge about all distributions, in our main results we do not consider scenarios where players have "insider" knowledge. If the insider knowledge is correct (i.e., is a refinement of the prior), then our mechanisms' revenue increases; see Appendix E. Still, how to aggregate even the incorrect information that the players may have about each other is a very interesting question for future studies.Another important direction is to elicit players' information for BIC mechanisms. For example, the BIC mechanisms in [23,10] are optimal in their own settings, and it is unclear how to convert them to information elicitation mechanisms.
Related WorkInformation elicitation. Following [35], information elicitation has become an important research area in the past decade [38,44,33]. A mechanism asks each player to report his private signal and his private knowledge about the prior distribution. The decision maker wants the mechanism to be BIC, and a player is rewarded based on his reported distribution and the other players' reported signals. Different from auctions, there are no allocations or prices, and a player's utility equals his reward. Proper scoring rules [9,22] are widely ...