Collusion With Persistent Cost Shocks
研究企业面临私有且随时间序列相关的成本冲击时，如何通过动态价格博弈达成最优合谋，发现成本完全相关时最优合谋方案会导致价格刚性，而成本不完全相关时部分生产效率最优。
We consider a dynamic Bertrand game, in which prices are publicly observed and each firm receives a privately observed cost shock in each period. Although cost shocks are independent across firms, within a firm costs follow a first-order Markov process. We analyze the set of collusive equilibria available to firms, emphasizing the best collusive scheme for the firms at the start of the game. In general, there is a tradeoff between productive efficiency, whereby the low-cost firm serves the market in a given period, and high prices. We show that when costs are perfectly correlated over time within a firm, if the distribution of costs is log concave and firms are sufficiently patient, then the optimal collusive scheme entails price rigidity: firms set the same price and share the market equally, regardless of their respective costs. Productive efficiency can be achieved in equilibrium under some circumstances, but such equilibria are not optimal. When serial correlation of costs is imperfect, partial productive efficiency is optimal. For the case of two cost types, first-best collusion is possible if the firms are patient relative to the persistence of cost shocks, but not otherwise. We present numerical examples of first-best collusive schemes.