High-frequency trading, also known as HFT, is a method of trading that uses powerful computer programs to transact a large number of orders in fractions of a second. It uses complex algorithms to analyze multiple markets and execute orders based on market conditions. Typically, the traders with the fastest execution speeds are more profitable than traders with slower execution speeds.
In addition to the high speed of orders, high-frequency trading is also characterized by high turnover rates and order-to-trade ratios. Some of the best-known high-frequency trading firms include Tower Research, Citadel LLC and Virtu Financial.
High-frequency trading became popular when exchanges started to offer incentives for companies to add liquidity to the market. For instance, the New York Stock Exchange (NYSE) has a group of liquidity providers called Supplemental Liquidity Providers (SLPs) that attempts to add competition and liquidity for existing quotes on the exchange. As an incentive to companies, the NYSE pays a fee or rebate for providing said liquidity. In November 2020, the average SLP rebate was $0.0012 for NYSE- and NYSE MKT-listed securities on NYSE.1 With millions of transactions per day, this results in a large amount of profits. The SLP was introduced following the collapse of Lehman Brothers in 2008, when liquidity was a major concern for investors.
The major benefit of HFT is it has improved market liquidity and removed bid-ask spreads that previously would have been too small. This was tested by adding fees on HFT, and as a result, bid-ask spreads increased. One study assessed how Canadian bid-ask spreads changed when the government introduced fees on HFT, and it was found that bid-ask spreads increased by 9%.2
HFT is controversial and has been met with some harsh criticism. It has replaced a number of broker-dealers and uses mathematical models and algorithms to make decisions, taking human decision and interaction out of the equation. Decisions happen in milliseconds, and this could result in big market moves without reason. As an example, on May 6, 2010, the Dow Jones Industrial Average (DJIA) suffered its largest intraday point drop ever, declining 1,000 points and dropping 10% in just 20 minutes before rising again. A government investigation blamed a massive order that triggered a sell-off for the crash.3
An additional critique of HFT is it allows large companies to profit at the expense of the "little guys," or the institutional and retail investors. Another major complaint about HFT is the liquidity provided by HFT is "ghost liquidity," meaning it provides liquidity that is available to the market one second and gone the next, preventing traders from actually being able to trade this liquidity.