Even a cursory review of the Antitrust Division's new Merger Guidelines reveals that they revolve around the concept of “concentration” and advance a particular method of measuring it – the Herfindahl-Hirschman Index. While concentration is scarcely a new idea in the antitrust treatment of...

An increasing body of empirical evidence is documenting trends toward rising concentration, profits, and markups in many industries around the world since the 1980s. Two major criticisms of these studies is that concentration and market shares are poorly measured at the national industry level...