This paper analyzes the Baron and Myerson’s (B–M) (Econometrica 50: 911–930 [1982]) scheme of monopoly regulation, a standard representative of Bayesian mechanisms. As is well known, the hboxB–M mechanism (and other related mechanisms) have as an explicit starting point the assumption that the regulator has an unchallenged prior belief about the cost function of the regulated monopolist.We analyze here the consequences resulting from the possibility that this prior belief may be subject to influence or manipulable. As we show in detail, under the B–M scheme, consumers and the regulated monopoly are highly sensitive to the regulator’s prior belief about the (private) cost information of the monopolist. Therefore, if a regulator’s beliefs are unaccountable to and unverifiable by a higher ity, the regulator has both the incentive and the possibility to change and/or misrepresent his prior belief when facing pressure or payoffs from interest groups representing consumers or the regulated firm. The results here show that the outcomes under a B–M mechanism favoring one or another interest group can vary over a wide spectrum. The results are consistent with capture theory and rent-seeking explanations of monopoly regulation and suggest the need to exercise care in using the insights and results of Bayesian regulatory theory to inform practice. Copyright Springer Science+Business Media, Inc. 2005
