Concentration and Geographic Proximity in Antitrust Policy: Evidence from Bank Mergers
研究发现，基于赫芬达尔指数的反垄断政策会遗漏邻近分支网络并购的反竞争效应，导致分支关闭等损害，而引入邻近性阈值可改善银行反垄断。
Antitrust often uses the Herfindahl-Hirschman Index (HHI) for merger screening and review. We argue that HHI-based antitrust policy using predefined markets in the banking industry misses anticompetitive effects that are predicted by the proximity of merging branch networks. Difference-in-differences estimates from thousands of mergers reveal that close-proximity bank acquisitions have harmful effects, including branch closures, even if they fall below the HHI threshold for enforcement. Neither lowering the threshold nor using narrower predefined markets addresses this underenforcement without introducing significant overenforcement and underenforcement of other transactions. However, using a proximity threshold to complement the HHI policy could improve bank antitrust.