Price volatility, international market links, and their implications for regulatory policies

Conclusions

The October 1987 stock market crash spawned an abundance of research papers, as scholars attempted to explain what seemed at the time, and to some extent remains, an inexplicable event.

Except for the period immediately around the crash, there is only meager evidence that international linkages across markets have become tighter over time. Yet the crash was worldwide in scope, and its similarity across countries was uncanny. Just on the face, this international similarity puts doubt to such explanations as particular macroeconomic events in one country, failure of a given country's market system, or simultaneous changes in underlying fundamentals (which were quite different across countries).

Assigning the origination of the crash to one country cannot be entirely ruled out, however, because of the possibility of a non-fully revealing equilibrium “contagion” process of the type suggested by King and Wadhwani (1988). Such a process would allow a world-wide crash to begin by a particular news event or even by a market “mistake” in one country. Evidence in favor of this process is that international correlations of returns increased dramatically during the crash period. However, this increase is consistent with other explanations, such as transaction costs hindering international arbitrage except during periods of high volatility.

Was the crash the bursting of a bubble? Some evidence seems to support this proposition: for example, in the majority of countries, the pre-crash period displayed significant serial dependence in stock returns, dependence that was definitely not present in the post-crash period. However, further work is necessary to ascertain whether this measured serial dependence is unusual relative to what one would have expected to find, even in a perfectly random process, by choosing a sample period that happened to culminate in a random peak. Ross (1987) shows that such ex post sample period selection will induce upward bias in estimates of serial dependence. Cross-country tests failed to detect this bias, but there are several ambiguities in the tests that will have to be resolved in future work.

The crash is history. What implications, if any, does it have for regulatory policy? Is there evidence that popular regulations or rules would have mitigated the crash, or that they would decrease price volatility in general? There is very little evidence in favor of the efficacity of margin requirements, price limits, or transactions taxes. Despite a large number of empirical studies, no one has provided evidence that margin requirements have an impact on volatility. There has been at least one recent paper claiming the contrary, but a careful examination of its methods have uncovered enough problems to cast those results into doubt.

As for price limits, there must be a very short-term impact on measured volatility, for the measured market price at a trading halt is likely to understate the direction of movement. Yet even for daily data, the cross-country evidence is slim that price limits reduce volatility, and there is no evidence at all that they work over periods as long as a week. In other words, trading halts caused by limits seem to have no effect on true volatility.

Transaction taxes are inversely but insignificantly correlated with volatility across countries, and the effect is too questionable for taxes to be used with confidence as an effective policy instrument.