Cost overrun and auction format in public works

We provide an empirical investigation of cost overruns in small public procurement projects, using a panel dataset of auctions held in the Italian Veneto region between 2004 and 2006. We use this sample to study the effect on cost overruns of auction formats (average bid as opposed to first price rule) conditional on the entry mechanisms (free as opposed to limited access). It is commonly believed that cost overruns are lower under average bid auctions telative to first price auctions. We find support to this believe only when access to the auction is limited. We interpret this findings as evidence that winner's adverse selection is an important problem in auctions for small size public works, and the lack of a significant effect of the average bid format in free entry auctions may reflect collusion.