Louis Kaplow, Market Definition Alchemy, 57 Antitrust Bull. 915 (2012).
Abstract: In a recent series of articles, I argue that the market definition/market share paradigm should be abandoned entirely. Among my central claims are that: (1) as a matter of economic logic, there exists no valid way to infer market power from the market shares in redefined (non-homogeneous-goods) markets — short of entirely reversing the market redefinition; and (2) choosing a best market requires already having in hand one’s best estimate of market power, rendering the exercise pointless — actually worse, since the market power inference from the chosen market is inferior to the estimate with which one began. Not surprisingly, criticisms advanced in this Symposium and elsewhere do not succeed in repealing the laws of logic, any more than medieval alchemists were able to overturn the laws of nature.