Over the past month, stock market indices have looked like a lot like a roller coaster, with 500 point swings either way, often on a daily basis.

The Dow Jones Industrial Average finished at 12,747 on July 21, fell to 10,719 on August 10, rebounded to 11,529, before dropping to 10,953. The Nasdaq stock index has experienced a similarly erratic ride.

Some observers say automated computer systems can be blamed for at least part of the accelerated unpredictability of the markets

"[The recent] volatility is absolutely crazy," said IDC analyst David O'Dowd. "I don't know a better way to put it. We've seen record lows to record highs in a span of days, not months or years," O'Dowd said. "That's what electronic markets have done."

Up to 70% of trading volume is now consummated by computerised high frequency trading systems, according to O'Dowd.

David Furlonger, an analyst at Gartner, said proprietary algorithms developed by hedge fund and other Wall Street firms are making decisions without human input. "That doesn't necessarily allow for more analytical, reasoned judgment by a human," he said.

Hedge fund management firms like Renaissance Technologies, Getco and Millennium-Traders are big users of automated trading systems, observers say.

Such firms generally build their own computer infrastructures and design proprietary algorithms that consider the timing, price and quantity of a trade order and then initiate the stock buy or sale, all without human intervention.

A little history

In 2003, analysts projected that the financial services industry would spend some $6 billion (£3.6 billion) over two years replacing manual workflows with a new scheme dubbed straight-through processing (STP) of trades.

In simple terms, STP is the replacement of manual processes with an unbroken electronic stream of information that travels from the broker/dealer systems to the clearing house. STP uses messaging standards, translation middleware and networks that link investment managers, broker/dealers, custodian banks and clearing houses.

In 2005, the New York Stock Exchange (NYSE) moved into the electronic exchange marketplace by merging with Archipelago Holdings, a pioneer electronic trader. The Nasdaq Stock Market followed suit by purchasing Instinet Group, the other leading US electronic trading company at the time.

Automatic problems

Fears that automated trading could cause problems have been fulfilled at times, such as last October when a so-called "flash crash" saw the Dow plunge by almost 1,000 points in a half hour, wreaking havoc on the financial markets.

An investigation by the Securities and Exchange Commission (SEC) and the Commodity Futures Trading Commission (CFTC) determined that automated trade execution caused the "flash crash." An SEC report said automated trade execution system had flooded the Chicago Mercantile Exchange's Globex electronic trading platform with a large sell order causing a panic among investors.

The Financial Industry Regulatory Authority (FINRA), the enforcement arm of the SEC, responded by enacting rules requiring a pause in the trading of individual stocks when the price moves 10% or more either way in a five minute period.