We model an online display advertising environment in which "performance'' advertisers can measure the value of individual impressions, whereas "brand" advertisers cannot. If advertiser values for ad opportunities are positively correlated, second-price auctions for impressions can be...

Market design applies economic principles to the often messy problems of real-world exchange in which goods may not be homogeneous, the identities of trading partners may matter, contracts may not be executed, and even the formulation of trade as balancing supply and demand may be unhelpful....