Mergers and coordinated effects

A merger is said to have coordinated effects if it results in more collusive outcomes. I review the theory of collusion, and the role played by communication in coordination. Mergers can affect the enforcement and participation constraints for a collusive agreement, and the selection from the equilibrium set of outcomes. I describe some recent empirical studies of the effects of mergers on collusion, and the underlying measurement issues associated with identifying the degree of coordination. I also discuss some recent cases in which coordinated effects were a concern, including both merger reviews and ex post investigations.