The stock market crash of October 1987 led to a boom in conferences, commissions, and studies of the stock market. In almost each case, the participants would try to understand the events of October 1987 by a detailed analysis or description of events during the particular days of high volatility. Of course, to us economists there was nothing qualitatively unusual about October 19, 1987; the stock market moved, and we have no model that succeeds in explaining the magnitude or sources of daily stock market volatility for that day or any other day. When asked by the National Bureau of Economic Research to organize yet another conference on this subject, I decided that it was time to put these events in a historical perspective and try to understand them in the context of longer time periods and broader models. The papers collected in this symposium issue admirably succeed in broadening...

[Changes in stock prices have substantial explanatory power for U.S. investment, especially for long-term samples, and even in the presence of cash flow variables. The stock market dramatically out-performs a standard q-variable because the market-equity component of this variable is only a rough proxy for stock market value. Although the stock market did not predict accurately after the crash of October 1987, the errors were not statistically significant. Parallel relationships for Canada raise the puzzle that Canadian investment appears to react more to the U.S. stock market than to the Canadian market.]

We investigate product-market competition when managers maximize shareholder value rather than their expected discounted value of profits. If shareholders are imperfectly informed about future profitability, shareholder-value maximization can lead to either more or less aggressive product-market strategies. Lower rivals’ profits lead investors to believe that the firm’s costs are low relative to those of its rivals and that the industry’s prospects are poor. If the former (latter) inference dominates, each firm tries to lower (raise) its rivals’ profits to increase its own stock price. We also consider implications for corporate financial structure.

[We investigate product-market competition when managers maximize shareholder value rather than their expected discounted value of profits. If shareholders are imperfectly informed about future profitability, shareholder-value maximization can lead to either more or less aggressive product-market strategies. Lower rivals' profits lead investors to believe that the firm's costs are low relative to those of its rivals and that the industry's prospects are poor. If the former (latter) inference dominates, each firm tries to lower (raise) its rivals' profits to increase its own stock price. We also consider implications for corporate financial structure.]

Changes in stock prices have substantial explanatory power for U.S. investment, especially for long-term samples, and even in the presence of cash flow variables. The stock market dramatically outperforms a standard q-variable because the market-equity component of this variable is only a rough proxy for stock market value. Although the stock market did not predict accurately after the crash of October 1987, the errors were not statistically significant. Parallel relationships for Canada raise the puzzle that Canadian investment appears to react more to the U.S. stock market than to the Canadian market.

[New evidence is provided on the determinants of stock-return variances. First, when the Tokyo Stock Exchange is open on Saturday, the weekend variance increases; weekly variance is unaffected, however, despite an increase in weekly volume. Second, the listing of U.S. stocks in Tokyo substantially increases the number of trading hours, but Tokyo volume is negligible for these U.S. stocks and their 24-hour variance is unaffected. The overall results are consistent with the predictions of private-information-based rational trading models, but inconsistent with both the irrational trading noise and public-information hypotheses.]

New evidence is provided on the determinants of stock-return variances. First, when the Tokyo Stock Exchange is open on Saturday, the weekend variance increases; weekly variance is unaffected, however, despite an increase in weekly volume. Second, the listing of U.S. stocks in Tokyo substantially increases the number of trading hours, but Tokyo volume is negligible for these U.S. stocks and their 24-hour variance is unaffected. The overall results are consistent with the predictions of private-information-based rational trading models, but inconsistent with both the irrational trading noise and public-information hypotheses.