Pairs trading, or statistical arbitrage (stat arb), is a classic, well-established quantitative trading strategy, and it is still in use today. I discussed its profitability in a previous post, and in this installment, we continue that discussion.
Pairs Selection Methods
Reference [1] provides a thorough review of the pairs trading literature between 2016 and 2023.
Pair selection is a critical step in pairs trading, and the paper offers a comprehensive review of the various pair selection methods used in practice. They are:
1-Distance Methods
Use SSE/SAE of normalized price differences to identify co-moving assets. Simple, intuitive, and historically profitable across markets, even after costs.
2-Cointegration Methods
Exploit long-run equilibrium relationships. Strong empirical support across equities and bonds, with advances in regime switching and external-factor integration.
3-Stochastic Control Methods
Model pairs trading as a continuous-time optimization problem. Incorporate jumps, regime changes, and stochastic volatility, showing strong performance but facing practical frictions.
4-Time Series Methods
Use GARCH, OU, and fractional OU to model short-term dynamics and volatility clustering. Adaptive thresholds improve returns; hybrid models are an emerging area.
5-Other Methods
Copulas capture tail dependence; Hurst exponent methods capture long memory; entropic approaches address model uncertainty. These improve robustness under nonlinear dynamics.
Overall, the review helps practitioners adapt stat-arb techniques to new markets and regimes. While simple methods once worked well, today’s competitive environment often requires more sophisticated approaches, though success still depends on model design, data quality, and market regime.
Profitability of Pairs Trading
There is an ongoing debate in the literature—some argue that “pairs trading is dead,” while others maintain that it remains profitable. From this review paper [1], we learn the following.
1- Pairs trading remains profitable, but returns are weaker and more conditional
The survey explicitly notes that profitability persists, but is not uniform and depends on market conditions, costs, and implementation details:
Empirical evidence consistently shows that distance-based pairs trading can be profitable across different markets, asset classes, and time horizons.
However, this is immediately tempered elsewhere by declining performance stability:
Performance is not uniform over time: profitability tends to vary with market volatility, and Sharpe ratios decline in certain subperiods.
- Transaction costs and competition materially erode profits
Modern profitability survives only after careful cost control, unlike the early 2000s results:
Even after accounting for realistic transaction costs, the strategy remains profitable in several markets.
- Advanced methods outperform naïve approaches
The paper makes clear that simple Gatev-style [2] implementations are no longer sufficient:
The apparent simplicity of GGR’s strategy becomes less evident as more sophisticated models and techniques have been introduced.
And later:
Regime-switching structures … demonstrate superior performance, particularly under frequent or pronounced regime shifts.
In short, the paper does not argue that pairs trading has stopped working, but it makes clear that the simple, mechanical versions that worked in the 1990s and early 2000s no longer deliver robust returns. Profitability today is weaker, highly dependent on market regimes, and much more sensitive to transaction costs and execution. What survives is not the original Gatev–Goetzmann–Rouwenhorst method, but more adaptive, model-driven implementations that account for changing volatility, correlations, and liquidity.
Reference
[1] Sun, Y. (2025). A survey of statistical arbitrage pairs trading strategies with non-machine learning methods, 2016-2023. WNE Working Papers, 19/2025 (482). Faculty of Economic Sciences, University of Warsaw
[2] Gatev, E., Goetzmann, W., & Rouwenhorst, K. G. (2006). Journal of Financial Economics, 81(1), 105–141.
Closing Thoughts
The paper provides a thorough review of all existing pair selection methods, which are critical to pairs trading. It also concludes that current profitability is weaker, highly dependent on market regimes, and significantly more sensitive to transaction costs and execution.