Herfindahl index(redirected from Herfindahl-Hirchman Index)
An index of market concentration the U.S. Department of Justice uses to determine whether a monopoly is forming. The scale goes from zero to 10,000, with 10,000 indicating that a single company controls 100% of the market share in a given industry. An HHI of less than 1000 indicates a market with little concentration, which the Justice Department prefers. Any merger or acquisition leading to an increase of more than 100 when the HHI was previously greater than 1,800 may lead to antitrust action against the company involved.