Circuit Breakers
The market collapse of October 19, 1987, prompted several suggestions for regulatory change. Among these was a call for “circuit breakers” to slow or stop trading during periods of extreme volatility. Some of the current circuit breakers still being used entail trading halts. If the Dow Jones Industrial Average falls by 10%, trading will be halted
or 1 hour if the drop occurs before 2:00 p.m. (Eastern Standard Time), for '/2 hour if the drop occurs between 2:00 and 2:30, but not at all if the drop occurs after 2:30. If the Dow falls by 20%, trading will be halted for 2 hours if the drop occurs before 1:00 p.m., for 1 hour if the drop occurs between 1:00 and 2:00, and for the rest of the day if the drop occurs after 2:00. A 30% drop in the Dow would close the market for the rest of the day, regardless of the time.
The idea behind circuit breakers is that a temporary halt in trading during periods of very high volatility can help mitigate informational problems that might contribute to excessive price swings. For example, even if a trader is unaware of any specific adverse economic news, if he sees the market plummeting, he will suspect that there might be a good reason for the price drop and will become unwilling to buy shares. In fact, he might decide to sell shares to avoid losses. Thus, feedback from price swings to trading behavior can exacerbate market movements. Circuit breakers give participants a chance to assess market fundamentals while prices are temporarily frozen. In this way, they have a chance to decide whether price movements are warranted while the market is closed.
Of course, circuit breakers have no bearing on trading in non-U.S. markets. It is quite possible that they simply have induced those who engage in program trading to move their operations into foreign exchanges.
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