Herfindahl-Hirschman Index

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.