No one has figured out the cause of the “flash crash”. Some background information might help, though, when we try to understand what happened.
- On May 6th, the Dow Jones Industrial Average plunged close to 1000 points, then made up some of its loss, and closed down 348. Most of the drop happened from 2:40 to 3:00.
- Historically, the New York Stock Exchange (NYSE) was the epicenter of buying and selling stock. Yes, there were other stock markets but the NYSE was king.
- Now, the NYSE is only one of many stock markets in which NYSE listed companies’ stock trade each day. For example, before 2003, Procter & Gamble shares were traded almost exclusively through the NYSE. Now, as shown on an Economist chart titled “Flash Crash Mish Mash,” Nasdaq, ArcaEx, Direct Edge, and BATS, and others also trade NYSE listed equities.
- Simplifying considerably, we can say that not only are stocks individually traded, but also “packages” of stocks are traded, and beyond that, people trade stocks that are based on stocks. And beyond all of this, not only are people buying and selling, but also, trying to make pennies on each transaction, we have computers doing very speedy trades with other computers. In fact, these high frequency trades now represent more than 60% of daily stock trading.
- Fundamentally, stock prices fall when the number of shares people (and computers) want to sell exceeds the amount people want to buy. If there is an avalanche of sell orders, the NYSE has slow down rules that are designed to let it maintain an orderly market. The other markets have (or don’t have) their own rules and no one necessarily has the same rules.
Can you see why no one knows why the Dow dove suddenly? And yet, to maintain investor confidence, regulators need to prevent it from happening again.
The Economic Lesson
The first rule of “Investing 101″ is, “Maintain an orderly market.” Orderly means that upward or downward price changes should unfold in steady increments; it means that trading will be halted whenever the buy or sell side becomes unmanageable. For several centuries “specialists” in trading posts on the floor of the NYSE were charged with maintaining orderly markets in the securities when they matched buyers and sellers. On May 6th, with no new news about the company, consulting firm Accenture’s stock tumbled 99% to one penny from above $40 a share and then returned to prior levels. Most of the drop occurred between 2:40 at 3:00. For Accenture, the market was not orderly.