The May 6 “flash crash” has put high frequency traders under a harsh spotlight. Many investors contend that these traders, who use high-tech tools to buy and sell stocks in microseconds, put long-term investors at a disadvantage by front-­running their orders and fueling market volatility. Such activity merely increases the effective cost of trading for pension funds and other institutional investors, critics say.

At a time when investors are struggling to eke out any returns they can get, costs are as important as ever. Fortunately, despite all the controversy about high frequency trading, the evidence suggests that these high-speed, high-­volume players continue to put downward pressure on equity transaction costs, not raise them, according to our 14th annual survey of trading costs, conducted for Institutional Investor by New York–based Elkins/McSherry, a subsidiary of Boston’s State Street Corp.

[Click here to access the tables indicating Global Trading, US Trading, Average Execution Time and Market Impact Trend.]

The average overall cost of equity trading in the U.S. edged up during the 12 months ended June 30, but that increase largely reflected lower trading volumes and higher volatility, says James Bryson, president of Elkins/McSherry. The underlying trend in costs is still headed lower, he adds. And costs fell significantly in most international markets.

“The concerns about high frequency trading are not justified, because we have seen trading costs falling pretty consistently,” says Jamie Ritchie, director of capital markets trading at Brockhouse & Cooper, a Montreal-­based global agency execution brokerage operating in 39 countries, including the U.S. “Some of that has to do with the high frequency traders.”

Average transaction costs for New York Stock Exchange–listed stocks rose 10 percent in the latest period, while costs on the Nasdaq Stock Market were up 16 percent, according to the survey. The U.S., with an overall average cost of equity trading of 19.63 basis points in the period, is no longer the world’s low-cost trading venue. Japan and Sweden share that crown, with an average cost of 18.34 basis points in the period, followed closely by France, at 18.49 basis points. Average transaction costs globally declined 8.1 percent over the past year, to 38.02 basis points.

Concern about high frequency trading soared after May 6, when the Dow Jones industrial average plunged nearly 600 points in a matter of minutes and temporarily erased $862 billion in equity value. A report on the incident by the Securities and Exchange Commission and the Commodity Futures Trading Commission attributed the collapse to a large automated sell order placed by a mutual fund manager, but it added that temporary withdrawals from the market by some high frequency trading firms may have exacerbated the decline. Regulators are weighing whether to impose some curbs on high frequency trading, but with such activity accounting for as much as 70 percent of stock trading volume in the U.S., the prospects of a crackdown appear remote.