Market power Market power is the des gree of control that a firm or group of firms has over the price and production decisions in an industry. o The monopolistic firm has a high degree of market power while perfectly competitive firms have no market power. Measures of market power: concentration ratio. Lerner's index herfindahl-Hirschman indexMarket Power  Market power is the degree of control that a firm or group of firms has over the price and production decisions in an industry.  The monopolistic firm has a high degree of market power while perfectly competitive firms have no market power.  Measures of market power: concentration ratio, Lerner’s index, Herfindahl-Hirschman index