|
The Herfindahl index (also known as Herfindahl–Hirschman Index, or HHI) is a measure of the size of firms in relation to the industry and an indicator of the amount of competition among them. Named after economists Orris C. Herfindahl and Albert O. Hirschman, it is an economic concept widely applied in competition law, antitrust〔''2010 Merger Guidelines'' § 5.3〕 and also technology management.〔Catherine Liston-Hayes, Alan Pilkington, (“Inventive Concentration: An Analysis of Fuel Cell Patents,” ) Science and Public Policy, (2004). Vol. 31, No. 1, p.15-25.〕 It is defined as the sum of the squares of the market shares of the firms within the industry (sometimes limited to the 50 largest firms),〔(Chapter 9 Organizing Production )〕 where the market shares are expressed as fractions. The result is proportional to the average market share, weighted by market share. As such, it can range from 0 to 1.0, moving from a huge number of very small firms to a single monopolistic producer. Increases in the Herfindahl index generally indicate a decrease in competition and an increase of market power, whereas decreases indicate the opposite. Alternatively, if whole percentages are used, the index ranges from 0 to 10,000 "points". For example, an index of .25 is the same as 2,500 points. The major benefit of the Herfindahl index in relationship to such measures as the concentration ratio is that it gives more weight to larger firms. The measure is essentially equivalent to the Simpson diversity index used in ecology and to the inverse participation ratio (IPR) in physics. ==Example== For instance, we consider two cases in which the six largest firms produce 90% of the goods in a market. In either case, we will assume that the remaining 10% of output is divided among 10 equally sized producers. * Case 1: All six of the largest firms produce 15% each. * Case 2: The largest firm produces 80% and the next five largest firms produce 2% each. The six-firm concentration ratio would equal 90% for both case 1 and case 2. But the first case would promote significant competition, where the second case approaches monopoly. The Herfindahl index for these two situations makes the lack of competition in the second case strikingly clear: * Case 1: Herfindahl index = (0.152+0.152+0.152+0.152+0.152+0.152) + (0.012+0.012+0.012+0.012+0.012+0.012+0.012+0.012+0.012+0.012)= 0.136 (13.6%) * Case 2: Herfindahl index = 0.802 + 5 * 0.022 + 10 * 0.012 = 0.643 (64.3%) This behavior rests in the fact that the market shares are squared prior to being summed, giving additional weight to firms with larger size. The index involves taking the market share of the respective market competitors, squaring it, and adding them together (e.g. in the market for X, company A has 30%, B, C, D, E and F have 10% each and G through to Z have 1% each). If the resulting figure is above a certain threshold then economists consider the market to have a high concentration (e.g. market X's concentration is 0.142 or 14.2%). This threshold is considered to be 0.25 in the U.S.,〔 while the EU prefers to focus on the level of change, for instance that concern is raised if there is a 0.025 change when the index already shows a concentration of 0.1.〔However, it gets far more complicated than that. See para. 16-21 ''Guidelines on horizontal mergers''〕 So to take the example, if in market X company B (with 10% market share) suddenly bought out the shares of company C (with 10% also) then this new market concentration would make the index jump to 0.162. Here it can be seen that it would not be relevant for merger law in the U.S. (being under 0.18) or in the EU (because there is not a change over 0.025). 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「Herfindahl index」の詳細全文を読む スポンサード リンク
|