"New Progress in Repeated Games: Implicit Collusion with Private Monitaring" (in Japanese)

The present paper provides a survey on the recent progress in the theory of repeated games. Many recent works investigated infinitely repeated games with discounting, and newly assumed that monitoring is private. These works provided their respective folk theorems or efficiency theorems on this assumption. In particular, it was shown in Matsushima (2001a) that in repeated prisoner dilemma games, approximate efficiency can be attained by a perfect equilibrium when private signals are conditionally independent and players are patient enough, irrespective of the accuracy of private monitoring technology. It was also shown in Matsushima (2001b) that in general two player games, approximate efficiency can be attained even though private signals are imperfectly correlated. The efficiency theorem can be applied to the study of cartel behavior with secret price cuts.