Mean Reversion II: Pairs Trading Strategies

Highlights

This Deutsche Bank research shows how to improve pairs trading with RavenPack’s news analytics. Their enhanced signal significantly reduces divergence risk and also boosts the average return per pair.

• The percentage of non-converged pairs dropped by about half from 15% to 7%.
• Average profit per pair increased from 2.3% to 2.8% for the European strategy, and from 1.6% to 1.9% for the US Strategy.
• Return distribution becomes more positively skewed.

Below is a pairs example for Sports Direct International plc and Dixons Carphone plc between November 2014 to January 2016.

Overall, the Sports Direct Intl price dropped by more than 40% over a period of two months. Clearly, trading the pair would have realized a loss. However, with access to a real-time news analytics feed, the loss could have been avoided by ignoring pair trades with price divergence supported by negative sentiment and abnormal news volume on either of the two companies (in this case, “Sports Direct Intl.”).

White Paper

In a previous report, Deutsche Bank discussed cross-sectional mean reversion strategies in equity markets. Pairs trading, which attempts to exploits a temporary mispricing between two securities with a stable relative price relationship, is another type of mean reversion strategy . In this report, Deutsche Bank show how you can improve both the selection and trading aspects of a conventional pairs trading strategy .

Fundamental risk models help to identify profitable pairs

Pairs trading strategies typically look for co-integrated relationships between stocks belonging to the same country and sector/industry group. They believe there are superior means with which to capture the degree of “fundamental similarity” between stocks. For example, they show that utilizing a fundamental risk model to identify stock pairs significantly reduces divergence risk, and also improves the average return per pair.

News analytics overlay to further enhance pairs trading performance

Divergence risk increases in the proportion of idiosyncratic risk associated with a pair's constituent stocks. A news analytics overlay which helps to differentiate between price divergence due to news as opposed due to random price movements, significantly improves the performance of the trading strategy by reducing the number of non-convergent trades.

Beyond stock pairs

In looking for potential pairs candidates, they do not have to limit ourselves to stock pairs. Deutsche Bank proposes a novel method based on clustering and dynamic tree-cutting to systematically identify clusters of stocks as potential constituents for synthetic pairs trading strategies.

Table of Contents

• Introduction
• Pairs Trading: The Basics
• Existing Pais Trading Approaches
• The Benchmark Strategy
• An Enhanced Pairs Trading Model
• Identifying Pairs Using a Fundamental Risk Model
• Applying A News Analytics Overlay to Pairs Trading
• An Addendum to Stock Pairs
• Conclusions
• References
• Appendix

Summarizing the Results

Peter Hafez - Chief Data Scientist - RavenPack

The principle of pairs trading is remarkably simple, but the devil is in the detail.

An investor finds assets whose prices moved together historically, open a trade by shorting the winner and buying the loser when the spread between them widens. The trade is closed when the spread converges. But that is not so simple...

Over the years, pairs trading has become one of the most popular statistical arbitrage strategies. The strategy exploits temporary anomalies between prices of assets that have some equilibrium relationship. While methods may differ in sophistication, all implementations rely on the use of statistical analysis of historical prices to identify pair candidates with stable inter-relationships.

The main challenge in building such strategies is that, often, cointegration between two assets breaks down out-of-sample – making the trade a losing proposition.

Fundamental Similarity

In an attempt to solve the challenge of cointegration breakdown, investors can benefit from looking for pairs that have some degree of “fundamental similarity”. Typically, pairs trading programs are looking for cointegration relationships between stocks belonging to the same country and sector/industry group.

However, In a recent study, Deutsche Bank utilized a risk model to proxy fundamental similarity. Overall, they found that taking such approach significantly reduced divergence risk across their portfolio, and also improved the average return per pair.

Differentiating Between “Good” and “Bad” Divergence

Even though fundamentally similar stocks are more likely to move in tandem in the near future, there are no guarantees for such behavior. Considering any single stock, a large proportion of the price movement is driven by idiosyncratic risk, which could permanently alter the equilibrium relationship between a company pair.

The profits and risks from trading stock pairs are very much related to the type of information event which creates divergence. If divergence is caused by a piece of news related specifically to one constituent of the pair, there is a good chance that prices will diverge further. On the other hand, if divergence is caused by random price movements or a differential reaction to common information, convergence is more likely to follow after the initial divergence.

To test the effects of news on a pairs trading strategy, Deutsche Bank used two aggregated indicators based on RavenPack’s Big Data analytics derived from news and social media data measuring sentiment and media attention. Specifically, using the two indicators, Deutsche Bank created a filter that would ignore trades where divergence was supported by negative sentiment and abnormal news volume. Figure 16, from the report, illustrates the pairs trading process with the news overlay.

Below is an overview of Deutsche Bank’s key findings - applying the RavenPack Big Data analytics overlay (see Figure 17):

• Lower Divergence Risk: the percentage of non-converged pairs dropped by over a half from 15% to 7%
• Higher Return: average profit per pair also increased from 2.3% to 2.8%, and the return distribution becomes more positively skewed
• Significant P-Values: the increase in average returns is confirmed by significant p-values (<0.05) from the one-sided pair-wise t-test

Figure 19, from the report, shows the results of the pairs strategies applied on the MSCI U.S. universe. As can be seen from the graph, the same conclusions can be reached, albeit the strategies have relatively lower returns in the U.S. The average return per pair under the benchmark strategy, the enhanced strategy using the risk model, and the final strategy with both risk model and news overlay are 0.2%, 1.6% and 1.9% respectively.

Overall, Deutsche Bank finds that applying a news analytics overlay can help differentiate between “good” price divergence (which is likely to converge) from “bad” divergence. More importantly, such ability provides significant improvements to the performance of a traditional pairs trading strategy, especially by reducing divergence risk.