Abstract
Auctions like sponsored search often implicitly or explicitly require that bidders are treated fairly. This may be because large bidders have market power to negotiate equal treatment, because small bidders are difficult to identify, or for many other reasons. We study so-called anonymous auctions to understand the revenue tradeoffs and to develop simple anonymous auctions that are approximately optimal.
We begin with the canonical digital goods setting and show that the optimal anonymous, ex-post incentive compatible auction has an intuitive structure — imagine that bidders are randomly permuted before the auction, then infer a posterior belief about bidder i’s valuation from the values of other bidders and set a posted price that maximizes revenue given this posterior.
We prove that no anonymous mechanism can guarantee an approximation better than \(\varTheta (n)\) to the optimal revenue in the worst case (or \(\varTheta (\log n)\) for regular distributions) and that even posted price mechanisms match those guarantees. Understanding that the real power of anonymous mechanisms comes when the auctioneer can infer the bidder identities accurately, we show a tight \(\varTheta (k)\) approximation guarantee when each bidder can be confused with at most k “higher types”. Moreover, we introduce a simple mechanism based on n target prices that is asymptotically optimal. Finally, we return to our original motivation and build on this mechanism to extend our results to m-unit auctions and sponsored search.
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Notes
- 1.
In some sense, the search engine would like to set a reserve price for the top slot. However, this must be carefully defined when no bidder meets the reserve price or when more than one bidder meets it; the decreasing price mechanism we discuss later in this paper may be considered a natural interpretation of setting different reserve prices for different slots in a sponsored search auction.
- 2.
Many factors, such as click-through-rates (CTRs) and relevance scores, will break symmetry in a sponsored search auction. As discussed in Ashlagi [3], these can be handled in a variety of ways, e.g. by requiring symmetry among bidders with the same CTR or score. We follow Ashlagi and consider a simple model without such parameters to avoid these complexities.
- 3.
Truthful reporting by the agents can be made an ex-post Nash Equilibrium by canceling the auction completely if an agent misreported his identity and the mechanism receives an identity twice.
- 4.
This is a regular VCG mechanism with a reserve price p.
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Tzamos, C., Wilkens, C.A. (2016). Anonymous Auctions Maximizing Revenue. In: Cai, Y., Vetta, A. (eds) Web and Internet Economics. WINE 2016. Lecture Notes in Computer Science(), vol 10123. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-54110-4_14
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DOI: https://doi.org/10.1007/978-3-662-54110-4_14
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