Pairs Trading

Pairs trading involves taking opposite positions in two related securities. You generally buy the relatively weaker security and sell the relatively stronger one when their price relationship moves away from its historical pattern.

• Pairs trading uses two related securities
• One position rises while another falls
• Traders watch changes in price spreads
• Mean reversion drives the basic strategy
• Past relationships may permanently break down
• Both trading legs carry separate risks

Pairs trading tries to make the difference between two securities more important than the direction of the overall market.

Suppose two companies operate in the same industry and their share prices have historically moved in a similar pattern. One share suddenly rises much faster than the other.

A pairs trader may believe this difference will reduce. The trader could buy the relatively weaker security and take a short position in the relatively stronger security.

If their prices move closer to their earlier relationship, the combined trade may generate a profit. If the gap widens instead, the trader can lose money.

This is why pairs trading is often described as a relative-value strategy.

Pairs trading is a strategy where you take opposite positions in two securities that have shown a meaningful historical relationship.

The securities may include shares, derivatives or exchange-traded funds.

Usually, one security is bought, creating a long position. The other is sold or shorted, creating the opposite position.

The aim is not simply to predict whether both prices will rise. You are trying to judge whether the price gap, or spread, between them will change.

Pairs trading is commonly linked with the idea of mean reversion. Mean reversion means that a price relationship that has moved away from its usual range may eventually move back towards it.

That movement is only an expectation. Historical relationships can change permanently.

The process starts by finding two securities whose prices have shown a stable relationship over a meaningful period.

Traders then study how the price difference between them normally behaves.

If the spread moves unusually far away from its historical range, a trader may consider taking opposite positions.

Here is the basic process:

Simply finding two securities with high correlation is not enough. Traders may also examine the stability of the spread and statistical relationships such as cointegration.

No. High correlation alone does not guarantee a successful pairs trade.

Correlation shows how closely two securities have moved together over a particular period. The correlation coefficient ranges from -1 to +1.

A value close to +1 means the securities have generally moved in the same direction. A value close to -1 means they have generally moved in opposite directions.

But correlation can change.

There is also no universal rule saying that a correlation above 0.80 automatically makes two securities suitable for pairs trading.

For example, two shares may show high correlation during one period because their whole sector is rising. A company-specific event may later cause their prices to behave very differently.

That is why experienced traders study the spread, business relationship, liquidity and stability of the historical relationship, rather than relying on one correlation number.

Choosing the securities carefully is one of the most important parts of pairs trading.

You can consider factors such as:

• Business relationship: Companies in similar industries may react to some common economic factors.
• Historical relationship: Check whether their price relationship has remained reasonably stable over different periods.
• Spread behaviour: Study whether past divergences have actually moved back towards a normal range.
• Liquidity: Both securities should have sufficient trading activity for entering and exiting positions.
• Company events: Earnings, mergers, regulation or business changes can permanently alter a historical relationship.
• Trading costs: Brokerage, taxes, borrowing costs and slippage can reduce the result from a small spread movement.

The purpose is to understand why the two securities move together, rather than selecting them only because a chart looks similar.

Consider a simple hypothetical example.

Ravi, a 32-year-old investor from Gwalior, has ₹1 lakh available for trading. He follows two hypothetical IT-sector shares, Stock A and Stock B.

The two shares have historically shown a relatively stable price relationship.

Stock A suddenly rises sharply after a short-term event, while Stock B remains almost unchanged. Ravi believes the gap may eventually narrow.

He considers:

• taking a long position in Stock B, and
• taking a short position in Stock A, where permitted.

Suppose the gap later narrows because Stock B rises relative to Stock A. The combined positions may generate a gain.

But suppose Stock A keeps rising because its business prospects have genuinely improved. The spread may widen further, producing a loss.

The example shows why historical relationships should not be treated as guarantees.

Pairs trading aims to reduce exposure to overall market direction, but it is not automatically completely market-neutral.

Imagine both securities fall because the broader market drops. Your short position may gain while your long position loses.

The two movements can partly offset each other.

But the protection may be incomplete. The securities may have different volatility, market sensitivity or position sizes.

One company could also face news that affects only its share price.

Therefore, pairs trading can reduce some directional market risk, but it cannot remove every type of trading risk.

A conventional pairs trade requires a long position and a short position.

Short selling means selling a security that you do not own at the time of the trade.

In India, the Securities and Exchange Board of India (SEBI) permits retail and institutional investors to short sell under its regulatory framework. Naked short selling is not permitted, which means settlement and delivery obligations must be honoured.

Securities Lending and Borrowing (SLB) provides a mechanism through which securities can be borrowed for delivery in eligible situations.

The exact method available to you can depend on the security, trading segment, broker and settlement requirements.

Pairs trading should therefore not be treated simply as a Margin Trading Facility strategy. Margin financing mainly relates to financing eligible purchases and does not by itself create both sides of a conventional long-short pairs trade.

Pairs trading can offer some useful characteristics when the strategy is properly researched.

• It focuses on relative price movement instead of only market direction.
• Opposite positions may reduce some broad-market exposure.
• It provides a structured way to trade price relationships.
• The strategy can be applied to different eligible instruments.
• Risk levels can be planned before entering.

These features do not mean that the strategy is low-risk. The performance of both positions still matters.

The biggest risk is simple: the expected price convergence may never happen.

Some important risks include:

• Relationship risk: Two securities may stop behaving as they did historically.
• Spread risk: The gap may continue widening after you enter.
• Liquidity risk: Low trading volumes may make an exit difficult or costly.
• Execution risk: The prices of both legs can change while you place the trades.
• Short-selling risk: The short position has its own settlement and borrowing requirements.
• Cost risk: Brokerage, taxes and other trading costs can reduce gains.
• Company-specific risk: Earnings, regulation or major corporate events can permanently change the relationship.

A stop-loss on only one leg may also change the risk of the remaining position. Both legs therefore need to be monitored together.

Start by deciding how much loss you are prepared to accept before entering the trade.

Do not assume that every divergence must reverse. First, understand why the gap has appeared.

You should also define:

1. the price or spread at which you enter,
2. the level at which you take profit,
3. the level at which you exit if wrong, and
4. the maximum capital you will put at risk.

Keep an eye on company announcements and sector developments while the position remains open.

If the reason for the historical relationship changes, continuing to wait for mean reversion can increase your loss.

Pairs trading lets you trade the price relationship between two securities rather than depending only on the market moving up or down. You take opposite positions and expect an unusual price gap to narrow. However, correlation does not guarantee convergence, and historical relationships can break permanently. Liquidity, execution costs, short-selling requirements and company-specific events also matter. Before using the strategy, understand both securities, study the spread carefully, set clear exit levels, and know how much capital you can afford to put at risk.