What does HHI mean in Unclassified?

Herfindahl–Hirschman index

The Herfindahl index (also known as Herfindahl–Hirschman Index, HHI, or sometimes HHI-score) is a measure of the size of firms in relation to the industry they are in and is an indicator of the amount of competition among them. Named after economists Orris C. Herfindahl and Albert O. Hirschman, it is an economic concept widely applied in competition law, antitrust and also technology management. HHI has continued to be used by antitrust authorities, primarily to evaluate and understand how mergers will affect their associated markets. HHI is calculated by squaring the market share of each competing firm in the industry and then summing the resulting numbers (sometimes limited to the 50 largest firms), market shares are expressed as either fractions, decimals, or whole numbers. The result is proportional to the average market share, weighted by market share. As such, it can range from 0 to 1.0, moving from a huge number of very small firms to a single monopolistic producer. Increases in the Herfindahl index generally indicate a decrease in competition and an increase of market power, whereas decreases indicate the opposite. Alternatively, if whole percentages are used, the index ranges from 0 to 10,000 "points". For example, an index of .25 is the same as 2,500 points. The major benefit of the Herfindahl index in relationship to such measures as the concentration ratio is that it gives more weight to larger firms. Other benefits of the Herfindahl index includes its simple calculation method and the small amount of easily obtainable data required for the calculation.The measure is the same formula as the Simpson diversity index, which is a diversity index used in ecology; the inverse participation ratio (IPR) in physics; and the inverse of the effective number of parties index in politics.

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