Economic Evidence in Antitrust: Defining Markets and Measuring Market Power

This paper addresses an important aspect of the interdisciplinary collaboration between law and economics: the use antitrust courts can and should make of empirical industrial organization economics, in light of the expansion of empirical knowledge generated during the last few decades. First we show how courts can apply what economists have learned about identification of alternative theories of industry structure and firm strategy to the problems of defining markets and determining whether market power has been exercised. We emphasize that the same analytic issues arise regardless of whether the evidence on these concepts is quantitative or qualitative. Second we show how courts can adopt a strategy employed in the research literature, by exploiting generalizations across closely related industries to help evaluate evidence and resolve cases. We also discuss ways of increasing the institutional capacity of the judicial system to make use of these two bodies of economic learning. These include a possible limited role for neutral economic experts in litigation, and a role for the antitrust enforcement agencies in identifying and codifying relevant generalizations about industries from the empirical economic literature to make that learning available to courts.