  Online bidding and auction are crucial aspects of the online advertising
industry. Conventionally, there is only one slot for ad display and most
current studies focus on it. Nowadays, multi-slot display advertising is
gradually becoming popular where many ads could be displayed in a list and
shown as a whole to users. However, multi-slot display advertising leads to
different cost-effectiveness. Advertisers have the incentive to adjust bid
prices so as to win the most economical ad positions. In this study, we
introduce bid shading into multi-slot display advertising for bid price
adjustment with a Multi-task End-to-end Bid Shading(MEBS) method. We prove the
optimality of our method theoretically and examine its performance
experimentally. Through extensive offline and online experiments, we
demonstrate the effectiveness and efficiency of our method, and we obtain a
7.01% lift in Gross Merchandise Volume, a 7.42% lift in Return on Investment,
and a 3.26% lift in ad buy count.
