In the U.S. today, there are sixteen exchanges for equities, commodities and options, as well as countless alternative trading venues (ATS) that include lightly regulated dark pools and brokers' own "internalizers" — matching engines that trade offsetting orders placed by a broker's customers. Each trading venue has its own approach to placing orders and navigating the methodologies is no easy feat. Among equity exchanges, for example, some use price-time priority and some pro-rata. Within the price-time priority category, some platforms are known as "normal," while others are "inverted." The differences are non-trivial, but luckily, not complicated, as I discuss in my new book, "High-Frequency Trading: A Practical Guide to Algorithmic Strategies and Trading Systems, 2nd edition."
"Normal" exchanges charge customers for placing "I-want-it-now-at-the-best-available-price" market orders and pay, yes, pay for "I-want-it-anytime-but-at-a-certain-price" limit orders. Inverted exchanges do the opposite: they charge for placing limit orders, yet compensate traders placing market orders. Both normal and inverted exchanges execute limit orders based on their respective price-time priority: the best-priced limit orders are executed before the worse-priced limit orders, and within each price queue, first-arrived limit orders are processed before limit orders that arrive later. In pro-rata markets, all best-priced limit orders are executed partially at the same time in equal proportion. Normal exchanges include NYSE, Direct Edge and BATS. NASDAQ Boston OMX, Direct Edge A, and BATS Y count among the inverted exchanges. Philadelphia stock exchange was operating under a pro-rata schedule until May 2013.
What my research shows is that pro-rata exchanges are the least susceptible to high-frequency market manipulation, while the normal exchanges are the most conducive to the said manipulation, with inverted exchanges falling somewhere in between, depending on their pricing. In a nutshell, the likelihood of manipulation is stemmed by potential costs of manipulation, be it the costs of being discovered, or the costs of executing an unintended trade. Furthermore, what my research shows is that the differences among the exchanges do not stop at market manipulation, but go much deeper into other areas frequently of concern to investors: market volatility, probability of market crashes and available liquidity. It turns out that structurally different markets exhibit different characteristics as far as all of these metrics are concerned.
[Is HFT Leveling the Playing Field?]
The normal exchanges tend to be more volatile and more prone to market crashes than their inverted and pro-rata brethren. As such, investors concerned about market manipulation may be best advised to execute their orders at inverted or pro-rata exchanges. At the same time, normal exchanges have built-in incentives for brokers to route their customers' orders there, making it all even more complicated!
Still, the explosion of exchange choices, however complex, gives today's investors an unprecedented ability to select their optimum exchange characteristics; fees, volatility, liquidity and probability of extreme events (crashes) being just a few of the parameters. For the first time in the history of financial markets, investors can choose the trading environment in which they feel most comfortable.
Irene Aldridge is an investment consultant, portfolio manager, a recognized expert on the subjects of quantitative investing and high-frequency trading (HFT) and a seasoned educator. Aldridge is currently Managing Partner and Quantitative Portfolio Manager at ABLE Alpha Trading, LTD., where designs, implements and deploys proprietary trading strategies. As part of her duties, Aldridge also advises broker-dealers, large hedge funds and government entities on high-frequency research and optimal strategy design, implementation of trading systems, and risk management and regulation of both high- and low frequency operations. At present, Aldridge has four HFT-related patents pending with the U.S. Patent and Trademark Office, and distributes real-time and near-real-time trading sentiment indicators to institutional subscribers via the AbleMarkets brand.