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In economics, a concentration ratio is a measure of the total output produced in an industry by a given number of firms in the industry. The most common concentration ratios are the CR4 and the CR8, which means the market share of the four and the eight largest firms. Concentration ratios are usually used to show the extent of market control of the largest firms in the industry and to illustrate the degree to which an industry is oligopolistic.〔(Concentration Ratios ), 16 December 2009〕 The standard tools of competition economists and competition authorities to measure market concentration are the Herfindahl index (HHI) and the concentration ratios (CR(n)).〔(London economics in association with global energy decisions: ''Structure and Performance of Six European Wholesale Electricity Markets in 2003, 2004 and 2005'', presented to DG Comp 26 February 2007 ), page 52 and page 8〕 These two are known as the traditional structural measures of market concentration (based on market shares). The concentration of firms in an industry is of interest to economists, business strategists and government agencies.〔(Industry Concentration ), 20 October 2009〕 == Two common ratios == * The Four-Firm Concentration Ratio measures the total market share of the four largest firms in an industry. * The Eight-Firm Concentration Ratio measures the total market share of the eight largest firms in an industry. Usually, these two common ratios are comparable from industry to industry, while concentration ratios for other numbers of firms can be also calculated.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「concentration ratio」の詳細全文を読む スポンサード リンク
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