An Explainer on How Market Concentration Is Measured

Concerns about market concentration and its effects on competition are at the heart of antitrust policy. Will Macheel explains the Herfindahl-Hirschman Index (HHI) as a common measure of market concentration, its implications for United States antitrust policy, and potential drawbacks of the measure. He closes the article by highlighting research on the HHI as a regulatory tool for screening mergers.