The Changing Behavior of Trading Volume Reactions to Earnings Announcements: Evidence of the Increasing Use of Accounting Earnings News by Investors

The increase in investor diversity over the last 35-40 years (ICI 2014) prompted us to revisit trading volume reactions to earnings announcements and how these reactions vary with firm size. This increase in investor diversity would likely lead to an increase in differences in the precision of pre-announcement information and potentially increase the importance of earnings announcements to resolve investor disagreement. We find that the nature of trading volume reactions to earnings announcements has fundamentally changed over the 35-year time period 1977-2011. There has been a dramatic increase in the magnitude and frequency of volume reactions to earnings announcements over this time period, and this effect is more pronounced in large firms where volume reactions were previously infrequent. The increase in large firms’ trading volume reactions is so pronounced that the relation between volume reactions and firm size has turned positive in recent years, thereby reversing Bamber’s (1986, 1987) previously documented negative relation. We provide intuition and empirical evidence that our results are attributable to the resolution of differential prior precision among an increasingly diverse set of investors following large firms.