Abnormal returns (market model prediction errors) are the subject of many event studies in accounting and finance literature. Conditional on the event of interest, researchers have recently used cross-sectional regressions to examine relations between abnormal returns and firm specific variables. This paper demostrates that non-constant variences and covariances in market model residuals across firms introduced bias in the estimated slope coefficients of the independent variables, i.e., the expected signs of the estimated slope coefficients can be predicted a priori. A method is develope to removed the bias in the estimated slope coefficiets and is found to be effective. This method explicitly takes the dependence among abnormal returns across firms into account. Methods that assume abnormal returns across firms to be independent do not control for such bias.

This paper documents the empirical distributions of daily trading volume prediction errors for several commonly used volume measures and expectation models for individual firms and for portfolios. The prediction errors for raw volume measures are significantly positively skewed, with thin left tails and fat right tails. However, natural log transformations of the volume measures are approximately normally distributed. For longer than one-day prediction intervals, recognition of autocorrelation in daily trading volume is advantageous for detecting abnormal trading. Results of analysis for clustering of events and for different size firms are also presented.

This paper provides evidence that repurchase tender offer announcements convey favorable information about the level and riskiness of future earnings. We show that analysts revise their forecasts of earnings per share upward following repurchase announcements. Repurchase announcement stock price reactions are positively correlated with revisions in short-term forecasts, but not correlated with revisions in long-term forecasts. Thus, the information is primarily about transitory changes in earnings. We also provide evidence that equity betas decline after repurchases. Our findings indicate that the equity beta decreases are due to decreases in the underlying riskiness of the firm's assets.