BETA, FIRM SIZE, AND CONCENTRATION

The asset beta of a firm is defined as the uncertainty about the firm's future value scaled by its current value. Empirically, beta is negatively related to a firm's size and concentration in its major product market. This relation has been interpreted as evidence that monopoly power affects beta. This paper shows that this empirical result is also consistent with competitive product markets where greater firm size and concentration are due to greater efficiency in production. Thus, the correlation between beta, firm size and concentration is not prima facie evidence of widespread monopoly power.