What Attracts Bidders to Online Auctions and What is Their Incremental Price Impact?

Abstract

Based on data from eBay auctions of classic comic books, we explore the determinants of the number of bidders in online auctions and the impact of additional bidders on the auction price. We test for winner's curse and examine how secret reserve prices impact both bidding activity and the auction price. In our data set, the number of bidders varies widely from zero in 20.4% of the observed auctions to ten or more in 16.5% but 70% of this variation in bidder numbers is predictable based on the comic being auctioned and attributes of the seller and auction such as third party certification of the comic's condition, the seller's reputation, and the length of the auction. Each additional bidder tends to increase the realized auction price about 2.4%. A minor part of this increase is apparently either because the auctions have a private value component or because some bidders fail to fully adjust for winners curse. However, most appears due to the inability of bidders to accurately determine the number of bidders they are bidding against. The presence of a secret reserve price sharply reduces the number of bidders in an auction but has little impact on what individual bidders are willing to bid.