Multiple Stochastically Stable Equilibria in Coordination Games

In an (n,m)-coordination game, each of the n players has two alternative strategies. A strategy generates positive payoff only if there are at least m-1 others who choose the same, where m>n/2. The payoff is nondecreasing in the number of such others so that there are exactly two strict equilibria. Applying the adaptive play with mistakes (Young 1993) to (n,m)-coordination games, we point out potential complications inherent in many-person games. Focusing on games that admit simple analysis, we show that there is a nonempty open set of (n,m)-coordination games that possess multiple stochastically stable equilibria, which may be Pareto ranked, if and only if m>(n+3)/2, which in turn is equivalent to the condition that there is a strategy profile against which every player has alternative best responses.