Beyond the Last Touch: Attribution in Online Advertising

Online advertisers often utilize multiple publishers and bid in multiple auctions concurrently to deliver ads, a process which may result in externalities between publishers that impact advertising effectiveness. In conjunction with these externalities, uncertainty about consumer visit patterns may limit the advertiser's ability to optimize its campaigns.We define the attribution problem as the attempt to measure such uncertainties and correct for the externalities, and determine the characteristics of a good attribution process. Using an analytical model of an online campaign we show that publisher externalities will lead an advertiser to shift from truthful bidding in equilibrium, and that combined with uncertainty about consumer visits, its profits will be lowered. Our analysis of a common attribution method known as last-touch shows that it reduces advertiser profits compared to not using attribution at all, and that stronger advertisers suffer from a misallocation of consumer impressions due to overbidding for ads resulting from the attribution process. Our analysis of an attribution scheme based on the Shapley value shows that it will improve the profits of advertisers when conversion rates in the market are not too high.