We document a seasonal pattern in stock returns around quarterly earnings announcement dates: small firms show large positive abnormal returns and a sizable increase in the variability of returns around these dates. Only part of the large abnormal returns can be accounted for by the tendency of firms with good news to announce early. Large firms show no abnormal returns around announcement dates and a much smaller increase in variability.

This paper develops and tests the uncertain information hypothesis as a means of explaining the response of rational, risk-averse investors to the arrival of unanticipated information. The theory predicts that following news of a dramatic financial event, both the risk and expected return of the affected companies increase systematically, and that prices react more strongly to bad news than good. An empirical investigation of over 9000 marketwide and firm-specific events produces results consistent with these predictions. We conclude that the market reacts to uncertain information in an efficient, if not instantaneous, manner.