Herfindahl-Hirshman index (HHI) a measure of the degree of dominance of a firm or firms in a market; the sum of squares of sales--HI = (size)2 + (size) 2 = … + (size) 2, where (size) 2 is the size of a firm squared






natural monopoly situation that exists when economies of scale persist throughout the entire market






per se rule a fixed rule of antitrust that an action is illegal no matter the circumstances






Rule of reason the idea that antitrust prosecution depends on the reasonableness of the action, that is, the circumstances surrounding the action

rent seeking devoting resources to transferring income from one group to another