David Glasner and Sean P. Sullivan on ‘The Logic of Market Definition’ (forthcoming) Antitrust Law Journal

This paper,available here , is not technically about merger control, but it is as relevant here as in any other competition topic – and it fits nicely with wider discussions of market power and market entry, which, as we have seen in past weeks, are common in merger control. While the usefulness of, and methodologies concerning market definition would seem to be well established, in practice both are actively questioned. Some have even argued that market definition is unnecessary in competition law. While this argument is not new, Louis Kaplow has recently advanced this thesis with a particularly pointed argument that: (1) market definition serves no role except to produce market shares, (2) market shares are poor measures of market power, and (3) antitrust would be better served by ignoring market shares and trying to assess market power from estimates of residual-demand curves and the like instead. The goal of this paper is to trace the internal logic of market…