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Pairs Trading Strategy

This pairs trading strategy monitors the price spread between two correlated instruments. By comparing the spread to its historical mean and standard deviation, the system attempts to exploit temporary divergences that eventually revert.

Testing indicates an average annual return of about 88%. It performs best in the stocks market.

A long spread is entered when the spread drops below its mean by more than the specified deviation multiplier. This means buying the first asset and selling the second. A short spread does the opposite when the spread rises above the mean by the same amount. Positions are closed once the spread returns to the average level.

Pairs trading appeals to market neutral traders who prefer relative-value opportunities rather than outright direction. Because both legs are hedged, volatility tends to be lower, though the strategy still uses a stop-loss on the spread to manage risk.

Details

  • Entry Criteria:
    • Long: Spread < Mean - Multiplier * StdDev
    • Short: Spread > Mean + Multiplier * StdDev
  • Long/Short: Both sides.
  • Exit Criteria:
    • Long: Exit when spread reverts to the mean
    • Short: Exit when spread reverts to the mean
  • Stops: Yes, percentage stop based on spread value.
  • Default Values:
    • LookbackPeriod = 20
    • DeviationMultiplier = 2.0m
    • StopLossPercent = 2m
    • CandleType = TimeSpan.FromMinutes(5)
  • Filters:
    • Category: Arbitrage
    • Direction: Both
    • Indicators: Spread statistics
    • Stops: Yes
    • Complexity: Intermediate
    • Timeframe: Intraday
    • Seasonality: No
    • Neural networks: No
    • Divergence: Yes
    • Risk Level: Medium
using System;
using System.Linq;
using System.Collections.Generic;

using Ecng.Common;
using Ecng.Collections;
using Ecng.Serialization;

using StockSharp.Algo.Indicators;
using StockSharp.Algo.Strategies;
using StockSharp.BusinessEntities;
using StockSharp.Messages;

namespace StockSharp.Samples.Strategies;
	
/// <summary>
/// Statistical Pairs Trading strategy.
/// Trades the spread between two correlated assets, entering positions when
/// the spread deviates significantly from its mean.
/// </summary>
public class PairsTradingStrategy : Strategy
{
	private readonly StrategyParam<int> _lookbackPeriod;
	private readonly StrategyParam<decimal> _deviationMultiplier;
	private readonly StrategyParam<decimal> _stopLossPercent;
	private readonly StrategyParam<DataType> _candleType;
	private readonly StrategyParam<Security> _secondSecurity;

	private SimpleMovingAverage _spreadMA;
	private StandardDeviation _spreadStdDev;
	
	private decimal _spread;
	private decimal _lastSecondPrice;

	/// <summary>
	/// Period for calculating mean and standard deviation of the spread.
	/// </summary>
	public int LookbackPeriod
	{
		get => _lookbackPeriod.Value;
		set => _lookbackPeriod.Value = value;
	}
	
	/// <summary>
	/// Number of standard deviations for entry signals.
	/// </summary>
	public decimal DeviationMultiplier
	{
		get => _deviationMultiplier.Value;
		set => _deviationMultiplier.Value = value;
	}
	
	/// <summary>
	/// Stop-loss percentage parameter.
	/// </summary>
	public decimal StopLossPercent
	{
		get => _stopLossPercent.Value;
		set => _stopLossPercent.Value = value;
	}
	
	/// <summary>
	/// Candle type parameter.
	/// </summary>
	public DataType CandleType
	{
		get => _candleType.Value;
		set => _candleType.Value = value;
	}
	
	/// <summary>
	/// Second security in the pair.
	/// </summary>
	public Security SecondSecurity
	{
		get => _secondSecurity.Value;
		set => _secondSecurity.Value = value;
	}
	
	/// <summary>
	/// Constructor.
	/// </summary>
	public PairsTradingStrategy()
	{
		_lookbackPeriod = Param(nameof(LookbackPeriod), 20)
			.SetGreaterThanZero()
			.SetDisplay("Lookback Period", "Period for calculating spread mean and standard deviation", "Parameters")
			
			.SetOptimize(10, 40, 5);
			
		_deviationMultiplier = Param(nameof(DeviationMultiplier), 2.0m)
			.SetGreaterThanZero()
			.SetDisplay("Deviation Multiplier", "Number of standard deviations for entry signals", "Parameters")
			
			.SetOptimize(1.5m, 3.0m, 0.5m);
			
		_stopLossPercent = Param(nameof(StopLossPercent), 2m)
			.SetGreaterThanZero()
			.SetDisplay("Stop-loss %", "Stop-loss as percentage of spread at entry", "Risk Management")
			
			.SetOptimize(1m, 3m, 0.5m);
			
		_candleType = Param(nameof(CandleType), TimeSpan.FromMinutes(5).TimeFrame())
			.SetDisplay("Candle Type", "Type of candles to use", "General");
			
		_secondSecurity = Param<Security>(nameof(SecondSecurity))
			.SetDisplay("Second Security", "Second security in the pair", "General")
			.SetRequired();
	}
	
	/// <inheritdoc />
	public override IEnumerable<(Security sec, DataType dt)> GetWorkingSecurities()
	{
		return
		[
			(Security, CandleType),
			(SecondSecurity, CandleType)
		];
	}
	
	/// <inheritdoc />
	protected override void OnReseted()
	{
		base.OnReseted();

		_spreadMA = null;
		_spreadStdDev = null;
		_spread = 0;
		_lastSecondPrice = 0;
	}

	/// <inheritdoc />
	protected override void OnStarted2(DateTime time)
	{
		base.OnStarted2(time);

		if (SecondSecurity == null)
			throw new InvalidOperationException("Second security is not specified.");
		
		// Initialize indicators
		_spreadMA = new() { Length = LookbackPeriod };
		_spreadStdDev = new StandardDeviation { Length = LookbackPeriod };
		
		// Create subscriptions for both securities
		var firstSecuritySubscription = SubscribeCandles(CandleType);
		var secondSecuritySubscription = SubscribeCandles(CandleType, security: SecondSecurity);
		
		// Bind to first security candles
		firstSecuritySubscription
			.Bind(ProcessFirstSecurityCandle)
			.Start();
		
		// Bind to second security candles
		secondSecuritySubscription
			.Bind(ProcessSecondSecurityCandle)
			.Start();
		
		// Enable position protection with stop-loss
		StartProtection(
			takeProfit: new Unit(0, UnitTypes.Absolute), // No take-profit
			stopLoss: new Unit(StopLossPercent, UnitTypes.Percent) // Stop-loss as percentage
		);
		
		// Setup chart if available
		var area = CreateChartArea();
		if (area != null)
		{
			DrawCandles(area, firstSecuritySubscription);
			DrawOwnTrades(area);
		}
	}
	
	private void ProcessFirstSecurityCandle(ICandleMessage candle)
	{
		// Skip if we don't have price for the second security yet
		if (_lastSecondPrice == 0)
			return;

		// Calculate the spread: Asset1 - Asset2
		_spread = candle.ClosePrice - _lastSecondPrice;
		
		// Process the spread through indicators
		var maValue = _spreadMA.Process(new DecimalIndicatorValue(_spreadMA, _spread, candle.ServerTime) { IsFinal = true });
		var stdDevValue = _spreadStdDev.Process(new DecimalIndicatorValue(_spreadStdDev, _spread, candle.ServerTime) { IsFinal = true });
		
		// Skip until indicators are formed
		if (!_spreadMA.IsFormed || !_spreadStdDev.IsFormed)
			return;
		
		decimal spreadMean = maValue.ToDecimal();
		decimal spreadStdDev = stdDevValue.ToDecimal();
		
		// Calculate entry thresholds
		decimal upperThreshold = spreadMean + (spreadStdDev * DeviationMultiplier);
		decimal lowerThreshold = spreadMean - (spreadStdDev * DeviationMultiplier);
		
		// Trading logic
		if (_spread < lowerThreshold)
		{
			// Spread is below lower threshold: 
			// Buy Asset1 (Security), Sell Asset2 (SecondSecurity)
			if (Position <= 0)
			{
				// Close any existing position and enter new position
				BuyMarket(Volume + Math.Abs(Position));
				LogInfo($"Long Signal: Spread({_spread:F4}) < Lower Threshold({lowerThreshold:F4})");
				
				// Note: In a real implementation, you would also place a sell order
				// for the second security here, using a different strategy instance or connector
			}
		}
		else if (_spread > upperThreshold)
		{
			// Spread is above upper threshold:
			// Sell Asset1 (Security), Buy Asset2 (SecondSecurity)
			if (Position >= 0)
			{
				// Close any existing position and enter new position
				SellMarket(Volume + Math.Abs(Position));
				LogInfo($"Short Signal: Spread({_spread:F4}) > Upper Threshold({upperThreshold:F4})");
				
				// Note: In a real implementation, you would also place a buy order
				// for the second security here, using a different strategy instance or connector
			}
		}
		else if ((_spread > spreadMean && Position > 0) || 
				(_spread < spreadMean && Position < 0))
		{
			// Exit signals: Spread returned to the mean
			if (Position > 0)
			{
				SellMarket(Math.Abs(Position));
				LogInfo($"Exit Long: Spread({_spread:F4}) > Mean({spreadMean:F4})");
			}
			else if (Position < 0)
			{
				BuyMarket(Math.Abs(Position));
				LogInfo($"Exit Short: Spread({_spread:F4}) < Mean({spreadMean:F4})");
			}
		}
	}
	
	private void ProcessSecondSecurityCandle(ICandleMessage candle)
	{
		// Store the close price of the second security for spread calculation
		_lastSecondPrice = candle.ClosePrice;
	}
}