## Cointegration and Pairs Trading in Stocks

**A related paper has been added to:**

#12 – Pairs Trading with Stocks

**Authors: **Do, Faff

**Title: **Cointegration and Relative Value Arbitrage

**Link:** http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2826190

**Abstract:**

We examine a new method for identifying close economic substitutes in the context of relative value arbitrage. We show that close economic substitutes correspond to a special case of cointegration whereby individual prices have approximately the same exposure to a common nonstationary factor. A metric of closeness constructed from the cointegrating relation strongly predicts both convergence probability and profitability in cointegration-based pairs trading. From 1962 to 2013, a strategy of trading cointegrated pairs of near-parity generates 58 bps per month after trading costs, experiences a 71% convergence probability and outperforms a strategy of pairs selected by minimized price distances.

**Notable quotations from the academic research paper:**

"In the pairs trading literature, the most common type of relative value arbitrage, substitutes for individual stocks are identified by minimizing the Euclidean distance in the daily price space over a historical period.5 Matching stocks over the price space instead of the return space is consistent with short-term relative value trading strategies, while removing the need to specify factors. Although the matching method is simple to perform, by design, it guarantees the existence of a counterpart for every stock, which is counterintuitive. More importantly, stocks that exhibit little variation in the price pattern over the formation period (possibly due to lack of news flow) would end up being labelled close substitutes, although they are not fundamentally related.

In this paper, we propose a simple method of identifying close economic substitutes using cointegration. When a pair of stock prices is cointegrated, one series co-moves with a scaled version of the other. We show that close economic substitutes can be represented by a system of cointegrated prices where the scaling factor, or the cointegration coefficient, is close to one.

We find that from 1962 to 2013, NonParity, a positive-valued metric of closeness that measures the distance of the cointegration coefficient from unity, strongly predicts both the probability that relative mispricing will subsequently be corrected as well as the profitability of the arbitrage trade. A one standard deviation increase in the variable reduces the convergence probability by seven percentage points and pairs trade payoffs by 2.78 percentage points. Further, predictability through NonParity also presents profitable trading opportunities. At the portfolio level, the pairs trading of cointegrated stocks is generally unprofitable. However, when trading is confined to pairs of stocks with NonParity close to zero, the strategy is profitable after reasonable estimates of brokerage, slippage, and short selling costs. Specifically, over the sample period, the average after-cost risk-adjusted return to trading a portfolio of cointegrated pairs with NonParity less than 0.5 (0.2) is 0.43% per month, with a t-statistic of 5.29 (0.58% per month, with a t-statistic of 4.77)."

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