The research question
The classic study reports historical performance for a simple distance rule. Later implementation must confront structural breaks, changing competition and costs that were less visible in early samples.
The useful question is not whether a chart once went up. It is whether the hypothesis has a clear economic mechanism, appears outside one hand-picked sample, can be reconstructed with information that was available at the time, and remains plausible after realistic implementation frictions.
Minimum viable rule
Form historically close price pairs, enter after a standardized divergence and exit when the spread converges or a risk limit is reached.
Universe: Liquid equities with dependable corporate-action and delisting data. A credible test fixes the universe, timestamps, missing-data policy and rebalance convention before model selection. Results should be shown both gross and net of an explicit cost model.
Implementation audit
Use formation and trading windows without overlap leakage. Adjust prices for corporate actions, model both legs, reject untradeable pairs, and include borrow, spread and market-impact costs.
At minimum, an audit should report turnover, worst peak-to-trough loss, recovery time, exposure concentration and sensitivity to neighboring parameter choices. A strategy that works only at one exact lookback or threshold deserves a lower level of confidence.
How the idea can fail
A divergence may reflect permanent information rather than temporary mispricing. Correlations can break, one leg can become hard to borrow, and crowded exits can amplify losses.
Failure conditions belong in the strategy definition. They provide a disciplined reason to investigate or stop, instead of changing the story after a loss.
Primary source
Pairs Trading: Performance of a Relative-Value Arbitrage Rule
Gatev, Goetzmann & Rouwenhorst (2006), Review of Financial Studies 19(3), 797–827.
DOI record
This page is an independent educational synthesis. It does not reproduce the paper and does not claim that published historical results are currently achievable.