R&Dインセンティブと特許期間の最適化-ノードハウス・モデルの構造と,その再考察-  [in Japanese] Incentives in R&D and the optimization of patent length: the structure of the Nordhaus model: a reexamination  [in Japanese]

This paper reconsiders the theory of the optimal patent length developed by Nordhaus(1969), and, by using Takahashi(2007), sheds new light on its implications for how best to benefit society. Patents, by protecting innovators from imitation, give them the incentive to bear the costs of their development efforts, and in doing so benefit society. However, it also works against benefitting society, since it makes the market monopolistic. This tradeoff can be mitigated by choosing the patent length carefully. The Nordhaus model successfully implies that, for maximizing social benefits, the patent length should be terminated in a finite period. He obtains this theoretical implication by assuming that any privately profitable innovation will benefit society, an idea that was first presented in Arrow(1962). In this article, these discussions are explained fully. Finally, this paper also shows that the optimal patent length may be zero for a minor innovation. This conjecture is derived from Takahashi(2007), and shows that Nordhaus' assumption does not hold when the innovation occurs in an oligopolistic market and the size of innovation is small.