The Cost of Capital and the Relevance of Non-diversifiable Risk

The conventional solutions to the corporate investment decision have been seriously challenged by recent developments in portfolio theory. In this paper, the author argues that, assuming the security market is composed of efficient diversifiers, there is no need, in the evaluation of investment projects, to adjust the time value of money to take account of risk. He concludes that the appropriate cut-off rate for any investment is equal to the yield on a 'risk-free' security such as undated or long-dated Government Stock.