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In law and economics, the Coase theorem (pronounced /ˈkoʊs/) describes the economic efficiency of an economic allocation or outcome in the presence of externalities. The theorem states that if trade in an externality is possible and there are sufficiently low transaction costs, bargaining will lead to an efficient outcome regardless of the initial allocation of property. In practice, obstacles to bargaining or poorly defined property rights can prevent Coasian bargaining. This "theorem" is commonly attributed to Nobel Prize laureate Ronald Coase during his tenure at the University of Chicago. However, Coase himself stated that the theorem was based on perhaps four pages of his 1960 paper "The Problem of Social Cost",〔http://www.coase.org/coaseinterview.htm〕 and that the "Coase theorem" is not about his work at all. This 1960 paper, along with his 1937 paper on the nature of the firm (which also emphasizes the role of transaction costs), earned Ronald Coase the 1991 Nobel Memorial Prize in Economic Sciences. In this 1960 paper, Coase argued that real-world transaction costs are rarely low enough to allow for efficient bargaining and hence the theorem is almost always inapplicable to economic reality. Since then, others have demonstrated the importance of the perfect information assumption and shown using game theory that inefficient outcomes are to be expected when this assumption is not met. Nevertheless, the Coase theorem is considered an important basis for most modern economic analyses of government regulation, especially in the case of externalities, and it has been used by jurists and legal scholars to analyse and resolve legal disputes. George Stigler summarized the resolution of the externality problem in the absence of transaction costs in a 1966 economics textbook in terms of private and social cost, and for the first time called it a "theorem." Since the 1960s, a voluminous amount of literature on the Coase theorem and its various interpretations, proofs, and criticism has developed and continues to grow. ==The theorem== Coase developed his theorem when considering the regulation of radio frequencies. Competing radio stations could use the same frequencies and would therefore interfere with each other's broadcasts. The problem faced by regulators was how to eliminate interference and allocate frequencies to radio stations efficiently. What Coase proposed in 1959 was that as long as property rights in these frequencies were well defined, it ultimately did not matter if adjacent radio stations interfered with each other by broadcasting in the same frequency band. Furthermore, it did not matter to whom the property rights were granted. His reasoning was that the station able to reap the higher economic gain from broadcasting would have an incentive to pay the other station not to interfere. In the absence of transaction costs, both stations would strike a mutually advantageous deal. It would not matter which station had the initial right to broadcast; eventually, the right to broadcast would end up with the party that was able to put it to the most highly valued use. Of course, the parties themselves would care who was granted the rights initially because this allocation would impact their wealth, but the end result of who broadcasts would not change because the parties would trade to the outcome that was overall most efficient. This counterintuitive insight — that the initial imposition of legal entitlement is irrelevant because the parties will eventually reach the same result — is Coase’s invariance thesis. Coase's main point, clarified in his article 'The Problem of Social Cost,' published in 1960 and cited when he was awarded the Nobel Prize in 1991, was that transaction costs, however, could not be neglected, and therefore, the initial allocation of property rights often mattered. As a result, one normative conclusion sometimes drawn from the Coase theorem is that liability should initially be assigned to the actors for whom avoiding the costs associated with the externality problem are the lowest. The problem in real life is that nobody knows ex ante the most valued use of a resource, and also that there exist costs involving the reallocation of resources by government. Another, more refined, normative conclusion also often discussed in law and economics is that government should create institutions that minimize transaction costs, so as to allow misallocations of resources to be corrected as cheaply as possible. * Version 1: A clear delineation of private property rights is an essential prelude to market transactions. * Version 2: As long as private property rights are well defined under zero transaction cost, exchange will eliminate divergence and lead to efficient use of resources or highest valued use of resources. * Version 3: The allocation of resources is invariant to the assignment of private property rights under zero transaction cost and zero income effect. 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「Coase theorem」の詳細全文を読む スポンサード リンク
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