資本費用과 投資의 Q模型

Cost of Capital and Q Model of Investment

This work incorporates the cost of capital into the marginal Q model of investment. The model described above features joint movements of the tax-adjusted marginal Q and investment in which firms’ profit and the cost of capital have an important role. In the model, firms maximize the present value of net profit, and we introduce the extensive tax policies in deriving marginal Q. The tax-adjusted marginal q is derived as the ratio of the marginal profit to the cost of capital. In this context, this marhinal q approach is distinctive from the average q approaches used in other works. In Korea marginal q had been widely distributed across industries because of different cost of caputal and tax incentives. Marginal q in the majority of industries had been less uhan one under the extensive tax incentives to investment, while the construction industry showed highest marginal q values. grsater than one. In this paper we find evidences that the tax-adjusted marginal q is significant variable in determining invetment, and the cost of capital is also an important signal in making a decision of capital stock. Hence, these results are cantrast to ones introduced from an accelerator model of investment.