Stable Observable Behavior

We study stable behavior when players are randomly matched to play a game, and before the game begins each player may observe how his partner behaved in a few interactions in the past. We present a novel modeling approach and we show that strict Nash equilibria are always stable in such environments. We apply the model to study the Prisoner's Dilemma. We show that if players only observe past actions, then defection is the unique stable outcome. However, if players are able to observe past action profiles, then cooperation is also stable. Finally, we present extensions that study endogenous observation probabilities and the evolution of preferences.