What Is Pairs Trading? - Fidelity (2024)

Trading strategy

Pairs trading is a strategy that tends to use statistics to identify relationships, assist in determining the direction of the relationship, and then ascertain how to execute a trade based on the data. The pairs trader attempts to capitalize on market imbalances between 2 or more financial instruments, such as stocks or funds, in anticipation of making money when the inequality is corrected.

To measure these relationships, the pairs trader will use statistics, fundamentals, technical analysis, and even probabilities. One of the main keys to pairs trading is finding strong correlations between financial instruments, thus building a foundation for further analysis. The empirical data are then dissected to unearth information that allows the trader an efficient and methodical way of executing successful trades.

Pairs trading is by no means a holy grail of trading and will have its ups and downs, like any other trading style.

Pairs work is based on a correlation between 2 (or more) stocks, sectors, indexes, or other financial instruments. Think of a highway and the service road that often runs parallel to it. Generally, the service road follows the highway closely but terrain or development will sometimes cause the 2 to diverge. The area between the highway and the service road can be thought of as the spread—the measured distance between the 2 objects traveling together. The pairs trader attempts to measure the spread with statistics in an effort to find a tradable relationship of inequality opportunities.

In a nutshell, pairs trading works by betting that 2 or more securities will diverge or converge in price. The trader bets that a $50 stock and a $55 stock, for instance, will either have a larger or smaller spread ($5 in this case) when the trade is closed. Divergence traders will like to see the spread increase while convergence traders will prefer to see the spread decrease.

Anyone can use pairs trading but it has tended to be employed by professionals and those with a good understanding of short selling. Transforming pairs trading from a theoretical construct into a practical reality capable of generating profits will involve several steps:

1. Formulate the selection criteria
2. Generate a list of candidate trades
3. Perform technical, fundamental, or other statistical overlays
4. Execute the trade
5. Manage the trade
6. Close the trade

The successful execution of each of the steps is a critical element in the process of becoming a profitable pairs trader. As is the case with any trading methodology, the complexity and success of the final 3 steps, the actual trading, are integrally dependent on the care and skill that go into the first 3.

Formulate the selection criteria

This is the most difficult and time-consuming step in the process. It includes selecting a trading universe, constructing and testing a model, if one is to be used, and creating general buy and sell guidelines. An individual trader's resources and expected trade duration will affect each of these factors, but the structure is functionally the same in all cases.

Determine the candidates

After a selection process has been defined, a trader must use that process to generate a list of candidate trades. If relying on manual research, the results of this inquiry constitute the list; if relying on a model, the model’s output serves as the list of candidates. The frequency of the procedure will also need to be considered. A trader who intends to hold a given position for several hours to several days will need to generate candidate trades with far greater frequency than a manager whose average holding period is measured in months.

The overlays

Pairs traders use some type of analysis methodology to confirm the trade and help customize the buy and sell rules. An overlay analysis will help adjust profit objectives and stop loss levels according to the specifics of a given trade. There are many different types of technical and fundamental overlays that can be employed, from candlestick charting to relative strength.

Execute the trade

While this would seem to be the most straightforward step in the investment process, there are a few subtleties. Generally speaking, the short side of a trade should be executed and filled before the long order is placed. In addition to the option of manually entering trades, there are some trading programs designed to handle pairs execution. These programs are designed to simultaneously work each side for the trader, particularly for larger orders, in an attempt to hit a pre-specified price ratio. For most traders, such programs are more of a convenience than a necessity because the slippage that occurs during execution is minimal relative to the profit objective of the overall trade.

Manage the trade

It is the responsibility of the trader to manage the position according not only to the predetermined buy and sell rules, but also to the changing market environment. The trader must be cognizant of the unexpected news releases affecting either of the instruments in a trade and be prepared to adjust their thinking accordingly. Likewise, they must be mindful of the pair's price action and constantly adjust the risk/return profile of the trade. For example, if a trade with an expected duration of 3 weeks were to achieve 50% of its profit objective in the first day after execution, the trader will want to reevaluate the potential reward for keeping the trade open. In such a situation, the trader could choose 1 of 2 options to prudently manage the trade moving forward. The trade could be immediately closed with a view that the additional return does not warrant the risk or the opportunity cost. The other option is to initiate a trailing stop loss level to lock in at least a portion of the profit. The trader will develop a feel for which of these options more suits their particular style, and may make different decisions for different pairs at different times.

Close the trade

For a trader who remains disciplined and follows the predetermined buy and sell rules as well as signals received from the market, closing the trade will be the easiest step. The most difficult criterion for a trader to adhere to is the duration limit. It is often difficult to close a trade that is losing a modest sum but has expired as the inclination is to opt to "give it a few days" in the hopes that the break-even level can be restored. The reward is usually larger losses or reduced profits, if only from the opportunity cost associated with not putting on other trades.

Pairs trading can be profitable but it requires significant research, close monitoring, clear rules, and discipline.