Abstract
This article experimentally examines two complex multi-unit auction mechanismsa simultaneous multi-round auction and its extension with combinatorial biddingthat offer the opportunity to communicate and thus collude. The general setting and parametrization originated in the 2013 Czech Spectrum Auction.
The results suggest that the package bidding format does not bring higher efficiency. Strikingly, allowing for communication increases efficiency in the examined auction formats.
A cheap-talk collusive agreement resulted in better allocation, as compared to the treatments without communication. The authors hypothesize that combinatorial bidding makes the decision-making of bidders too complicated and causes inefficiency, especially in auctions with large numbers of goods.