This paper presents a model of stock price reactions to partially anticipated events. The model formalizes the intuition that stock price reactions reflect both the economic importance of events and the extent to which events are surprises. Unbiased estimates of the economic importance of partially anticipated events must combine stock price reactions to events with stock price movements in periods when no event occurs. The model is used to estimate the value of acquisition attempts made by frequently acquiring firms. For a sample of thirty active acquirers, the evidence indicates that acquisition attempts were profitable investment projects.

This paper measures the effects on stock proces of corporate investments in 5% or more of another company's equity securities. Such investments initiate a process that may end with a takeover, targeted repurchase, takeover by a third party, or sale of the shares. The total valuation effect of the investment for acquiring and target firms includes returns at disclosure of the investment position, the outcome announcement, and related intervening events. For example, the positive return for target firms at initial disclosure of the investment more than offsets the negative return at a targeted repurchase.

This study does not support the view that a large number of shares can be sold at the prevailing market price and at a small cost. A significant stock price decrease is observed at the initial announcement of secondary distributions. The price declines are greater for offerings by officers and directors and for larger offerings, but are significant for all types of sellers and for large and small offerings. There is no significant price decline at the offering when secondaries are announced in advance. Underwriting and other selling costs are substantial and are positively related to relative offering size.

This paper analyzes the empirical behavior of stock-return volatilities prior to and subsequent to the ex-dates of stock splits. The evidence demonstrates rather unambiguously that there is, on the average, an approximately 30% ‘arbitrary’ increase in the return standard deviations following the ex-date. The increase holds for both daily and weekly data, and it is not temporary. No explanatory confounding variables, such as institutional frictions affecting price observations, have been identified. We view the findings as being essentially inconsistent with the notion of ‘rational pricing’.