DEPARTMENT OF ECONOMICS MINIMAX REGRET AND STRATEGIC UNCERTAINTY Ludovic Renou, University of Leicester, UK Karl H. Schlag, Universitat Pompeu Fabra, Spain Working Paper No. 08/2 January 2008 Updated April 2008 Minimax regret and strategic uncertainty∗ Ludovic Renou † University of Leicester Karl H. Schlag ‡ Universitat Pompeu Fabra April 22, 2008 Abstract This paper introduces a new solution concept, a minimax regret equilibrium, which allows for the possibility that players are uncertain about the rationality and conjectures of their opponents. We provide several applications of our concept. In particular, we consider price- setting environments and show that optimal pricing policy follows a non-degenerate distribution. The induced price dispersion is consis- tent with experimental and empirical observations (Baye and Morgan (2004)). Keywords: minimax regret, rationality, conjectures, price disper- sion, auction. JEL Classification Numbers: C7 ∗We thank Pierpaolo Battigalli, Gianni De Fraja, Pino Lopomo, Claudio Mezzetti, Stephen Pollock, Luca Rigotti, Joerg Stoye, and seminar participants at Barcelona, Birm- ingham, and Leicester for helpful comments. Renou thanks the hospitality of Fuqua Business School at Duke University. †Department of Economics, Astley Clarke Building, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom.
[email protected] ‡Department of Economics and Business, Universitat Pompeu Fabra,
[email protected] 1 1 Introduction Strategic situations confront individuals with the delicate tasks of conjec- turing other individuals’ decisions, that is, they face strategic uncertainty. Naturally, individuals might rely on their prior information or knowledge in forming their conjectures. For instance, if an individual knows that his oppo- nents are rational, then he can infer that they will not play strictly dominated strategies.1 Furthermore, common knowledge in rationality leads to rational- izable conjectures (Bernheim (1984) and Pearce (1984)).