We analyze the optimal dynamic policy of an antitrust authority toward horizontal mergers when merger proposals are endogenous and occur over time. Approving a currently proposed merger may affect the profitability and welfare effects of potential future mergers, whose characteristics may not yet be known. We identify conditions under which discounted expected consumer surplus is maximized by using a completely myopic merger review policy that approves a merger if and only if it does not lower consumer surplus given the current market structure. We also discuss a number of extensions as well as factors that undermine the optimality of myopic merger review policies.

National audience

We develop a theory of collective brand reputation for markets in which product quality is jointly determined by local and global players. In a repeated game of imperfect public monitoring, we model collective branding as an aggregation of quality signals generated in different markets. Such aggregation yields a beneficial informativeness effect for incentivizing the global player. It however also induces harmful free-riding by local, market-specific players. The resulting trade-off yields a theory of optimal brand size and revenue sharing that applies to platform markets, franchising, licensing, umbrella branding, and firms with team production.

We study merger policy in a dynamic computational model in which firms can reduce costs through investment or through mergers. Firms invest or propose mergers according to the profitability of these strategies. An antitrust authority can block mergers at some cost. We examine the optimal policy for an antitrust authority that cannot commit to its future policy and approves mergers as they are proposed. We find that the optimal policy can differ substantially from a policy based on static welfare. In general, antitrust policy can greatly affect firms’ investment behavior, and firms’ investment behavior can greatly affect the optimal antitrust policy.