an index ranging in value from 0 to 10,000 indicating the concentration in an industry; it is calculated by summing the squares of the market shares of all the firms in the industry.

A measure for assessing the degree of market concentration, this index is useful for the administration of antitrust policy. If the sum of the squared market shares of the firms in a given market exceeds some fixed quantity, such as 1,800, further merger activity might be disallowed by antitrust administrators.

A formula for defining market concentration by summing the squares of the individual market shares of all participants.