Market Shares And Rules Of Thumb

Abstract

Several popular propositions about firms’ market shares influence antitrust enforcement, legislation, and business practices.  These propositions, however, may not always reflect reality.  This paper explores exception to the rules that a broadened product market definition benefits the defendant in a monopolization case, that excess capacity and high seller concentration are unlikely to occur in the same market, and that vertical price restraints benefit full price sellers at the expense of their discounting competitors.