Presentation on theme: "Internet Advertising and the Generalized Second-Price Auction: Selling Billions of Dollars Worth of Keywords BENJAMIN EDELMAN, MICHAEL OSTROVSKY, AND MICHAEL."— Presentation transcript:
1Internet Advertising and the Generalized Second-Price Auction: Selling Billions of Dollars Worth of KeywordsBENJAMIN EDELMAN, MICHAEL OSTROVSKY, AND MICHAEL SCHWARZAmerican Economic Review, vol. 97(1), March, 2007Bo Zhou
2Generalized First-Price Auction Advertisers get positions according to their bids. Each one pays exactly the amount of his or her bid for each click.Suppose we have three bidders and two advertising positions with CTRs of 200 and 100, respectively.AdvertiserPer-click ValueBidPayoffWindows104.011198Mac42.01199Linux2
3Generalized First-Price Auction But smart advertisers always try to minimize costs.AdvertiserPer-click ValueBidPayoffWindows102.021596Mac42.01199Linux2AdvertiserPer-click ValueBidPayoffMac102.03394Windows42.02798Linux2
4Generalized First-Price Auction Using GFP, the auction can be extremely volatile, even chaotic. Bidders have strong incentives to “game” the system by slightly outbidding the advertiser right above. The ad sellers ultimately swallow the loss.Consider the following example in which Windows employs a bidding robot while both Mac and Linux bid manually.AdvertiserPer-click ValueBidPayoffWindows102.021596Mac42.01199Linux2
5Vickrey–Clarke–Groves Auction (VCG) Advertisers get positions according to their bids. Each one pays the “externality” he or she imposes on others by taking one slot away.ABCDACDB should pay what C and D lose.AdvertiserPer-click ValueBidPaymentPayoffWindows106001400Mac4200Linux2
6VCG Auction Truth-telling is a dominant strategy under VCG. A dominant strategy performs at least as well as any other strategy in any situation.Simply put, it is one of your best responses to the auction.Still, ad seller’s revenue suffers.
7Generalized Second-Price Auction Advertisers get positions according to their bids. Each one pays the amount of bid of the advertiser right blew for every click.Consider the following example where everybody bids truthfully.AdvertiserPer-click ValueBidPaymentPayoffWindows1041200Mac2200LinuxIt appears that nobody has any incentive to shift bidding strategy because nobody will be better off by doing so!
8Generalized Second-Price Auction This situation is called an equilibrium. In an equilibrium, everyone chooses the best strategy by taking into account every other’s strategy. In other words, nobody can be better off by shifting strategy unilaterally.The example on the last slide shows that using truth-telling strategy under GSP can produce equilibrium. From an bidder’s perspective, using truth-telling strategy under GSP can maximize its payoff.Just sometimes!!!
9Generalized Second-Price Auction Let’s consider a similar example where the CTRs of both positions are now 200 and 199.If all three bidders stick to the truth-telling strategy.AdvertiserPer-click ValueBidPaymentPayoffWindows1041200Mac2200LinuxHowever, what if Windows decides to change course?AdvertiserPer-click ValueBidPaymentPayoffMac43200Windows1021600Linux
10Locally envy-free Equilibrium Equilibrium looks fine, but is it stable?Not necessarily.An advertiser may have incentives to behave aggressively to swap positions with the advertiser right above him or her.
11Locally envy-free Equilibrium Now CTRs change to 300 and 100, respectively.AdvertiserPer-click ValueBidPaymentPayoffWindows54300Mac63LinuxMac wants to provoke.AdvertiserPer-click ValueBidPaymentPayoffWindows54.993Mac6300Linux
12Locally envy-free Equilibrium Apparently, Windows would like to retaliate.AdvertiserPer-click ValueBidPaymentPayoffMac64.994.98306Windows53198LinuxLocally envy-free equilibrium is an equilibrium where no advertiser has any incentive to swap positions with the advertiser right above him or her.Locally envy-free equilibrium is stable.
13Locally envy-free Equilibrium Construct a particular locally envy-free equilibrium where all advertisers’ payments coincide with their payments in truth-telling equilibrium in VCG.Advertisers are labeled in decreasing order of their values, i.e., if 𝑗<𝑘, then 𝑠 𝑗 ≥ 𝑠 𝑘 .𝑏 𝑘 = 𝑝 𝑉, 𝑘−1 / 𝛼 𝑘−1 , 𝑏 1 = 𝑠 1𝑏 𝑘 is advertiser k’s bid; 𝑝 𝑉, 𝑘−1 is the payment of advertiser k-1 in the truth-telling strategy equilibrium of VCG; 𝛼 𝑘−1 is position k-1’s CTR.AdvertiserPer-click ValueBidPaymentPayoffWindows1031400Mac42200Linux
14A little history Generalized First-Price Auction GoTo (now called Overture under Yahoo!) invented GFP auction in It probably marked the start of pay-per-click era of Internet advertising.VCG AuctionIt was first proposed by Vickery in 1961.I have not found any evidence suggesting it was used by any major search engine.Generalized Second-Price AuctionGSP was first introduced by Google in Yahoo! switched to GSP soon after.
15Why GSP, not VCG?VCG seems to be such an elegant mechanism. In fact, William Vickery won a Nobel Prize for it.GSP appeared first. So, it has the upper hand.VCG is hard to explain.Switching is expensive.Revenue prospects are uncertain.