Skewed Bidding in Per Per Auction Models of Online Advertising

Online search, as well as keyword-based contextual advertising on third-party publishers, is primarily priced using pay-per-click: advertisers pay only when a consumer clicks on the advertisement. Slots for advertisements are auctioned, and per-click bids are weighted by the probability of a click given that the advertisement is displayed (the click-through rate) in addition to other factors.