Using Jump-Diffusion Return Models to Measure Differential Information by Firm Size

Abstract

Portfolios of stocks issued by small firms are well known to earn rates of return in excess of those commensurate with their market sensitivities. One common explanation for this phenomenon is that small firm stocks are riskier than large firm stocks because less information is available about the former than about the latter. A necessary condition for such an explanation to be valid is that the information effect not be eliminated by combining the individual stocks into portfolios. This paper uses jump-diffusion return models to gauge the impact of information by firm size. The results show that portfolios of small firm stocks are no more prone to information surprises than are portfolios of large firm stocks. However, portfolios of small firm stocks are found to react more severely than portfolios of large firm stocks when surprises do occur.