FOUR-FIRM CONCENTRATION RATIO: The proportion of total output in an industry that's produced by the four largest firms in the industry. This is one of two common concentration ratios. The other is the eight-firm concentration ratio. The four-firm concentration ratio is commonly used to indicate the degree to which an industry is oligopolistic and how market control is held by the four largest firms in the industry. See also | concentration ratio | eight-firm concentration ratio | market share | market control | oligopoly | monopolistic competition |
