Round Bidding in Auctions

Our analysis of novel data from hundreds of thousands of online auctions on a large platform operating in the Netherlands uncovers a tendency to bid round numbers. Round winning bids are higher than average for a given item and are eschewed by bidders as they gain experience. These findings lead us to hypothesize that, rather than delivering a strategic benefit (say, adding salience to a jump bid), round bidding is a symptom of a behavioral bias. We construct a structural model of behavioral bidding in auctions, estimated for each of a subsample of the most frequently auctioned items. Our median estimate is that 21% of bidders are prone to round-number bias, reducing their expected surplus by nearly 10%.