Standard Bayesian models assume agents know and fully exploit prior distributions over types. We are interested in modeling agents who lack detailed knowledge of prior distributions. In auctions, that agents know priors has two consequences: (i) signals about own valuation come with precise...

This short paper shows that in an affiliated value setting one more bidder at the auction stage need not induce a higher expected welfare in either ascending price or second price auctions. We highlight the roles of asymmetries between bidders and of the multidimensional character of the private...