Systematic risk and the theory of the firm: A reexamination

A recent microeconomic model of the determinants of equity betas (Subrahmanyam and Thomadakis 1980) is generalized by including risky human capital in the market portfolio and allowing a general covariance structure between the model's sources of uncertainty. This provides an explanation of the ambiguous effect of operating leverage on beta by viewing human capital and equity contributors as risk sharers in the firm's output risk. This explanation may help to clarify the apparent conflict with the previous literature. The relationship between systematic risk and monopoly power is rederived and shown to depend upon a plausible condition on the correlation between wage rate and price uncertainty. Finally, the public policy implications of this analysis are presented.