The Changing Nature of Trading Volume Reactions to Earnings Announcements: Further Evidence of an Increase in Pre-Announcement Private Information

We document a change in the nature of trading volume reactions to quarterly earnings announcements over the time period 1976-2005. Consistent with Landsman and Maydew (2002), we find that the magnitude of abnormal trading volume around quarterly earnings announcements has increased over time and that this increase is greater for large firms than small firms. We show, however, that this trend has reversed the negative relation between firm size and trading volume documented by Bamber (1987). Applying insights from recent trading volume theory, we predict and provide evidence that the increase in abnormal trading volume across time and firm size is due to increases in pre-announcement private information. Specifically, we show that the component of abnormal trading volume associated with price change, which theory suggests reflects pre-announcement private information, is increasing across time and firm size. Our results suggest that investors are motivated to acquire private information prior to earnings announcements about firms that have relatively high quality information environments. Thus, our results have implications for policies aimed at reducing information asymmetry between investors by increasing public disclosure.