No abstract

This study examines changes in stock liquidity, as measured by the bidask spread, when a stock is added to the S&P 500 Index. The paper presents evidence of a significant decrease in the bidask spread upon S&P 500 addition, however, this effect is limited to only those stocks that were not trading listed options. Further, the decrease in the bidask spread for nonoptioned stocks is accompanied by a significant and permanent increase in share price and trading volume. While optioned stocks experience a permanent increase in trading volume, they experience only a temporary increase in share price. The findings for optioned stocks support the hypothesis that the price and volume effects associated with S&P 500 addition derive from temporary price pressure. Findings pertaining to the nonoptioned stocks indicate that the price and volume effects associated with S&P addition reflect enhanced stock liquidity. The decrease in the bidask spread for nonoptioned stocks is attributed to informational efficiencies achieved via index arbitrage trading, and it is argued that this effect is mitigated for optioned stocks due to the pre-existence of arbitrage trading between the option and the underlying stock.(the editor) and an anonymous referee for useful comments on earlier drafts. We also thank Upinder Dhillon and other participants at the 1995 FMA meetings for helpful suggestions and discussions.

We examine the extent to which announcements of open market share repurchase programs affect the valuation ofcompeting firms in the same industry. On average, although firms announcing open market share repurchase programs experience a significantly positive stock price reaction at announcement, portfolios of rival firms in the same industry experience a significant and contemporaneous negative stock price reaction. This suggests that perceived changes in the competitive positions of the repurchasing firms occur at the expense ofrival firms and dominate any signals of favorable industry conditions. Thus, the competitive intra-industry effects of open market repurchases outweigh any contagion effects. In addition, cross-sectional tests indicate that these competitive effects are more pronounced in industries characterized by a lower degree of competition and less correlation between the stock returns of the repurchasing firm and its rivals.

No abstract

Workers exposed to metallic mercury vapor were subjects for EMG, hand tremor and psychomotor tests conducted over an eighteen month period. Performance decrements in neuromuscular functions and psychmotor skills were found to be reversible and correlated with blood and urine mercury levels.