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Bollinger Width Mean Reversion

The Bollinger Width Mean Reversion strategy focuses on extreme readings of the Bollinger to exploit reversion. Wide departures from the average level rarely last.

Testing indicates an average annual return of about 157%. It performs best in the crypto market.

Trades trigger when the indicator swings far from its mean and then begins to reverse. Both long and short setups include a protective stop.

Suited for swing traders expecting oscillations, the strategy closes out once the Bollinger returns toward balance. Starting parameter BollingerLength = 20.

Details

  • Entry Criteria: Indicator crosses back toward mean.
  • Long/Short: Both directions.
  • Exit Criteria: Indicator reverts to average.
  • Stops: Yes.
  • Default Values:
    • BollingerLength = 20
    • BollingerDeviation = 2.0m
    • WidthLookbackPeriod = 20
    • WidthDeviationMultiplier = 2.0m
    • AtrPeriod = 14
    • AtrMultiplier = 2.0m
    • CandleType = TimeSpan.FromMinutes(5)
  • Filters:
    • Category: Mean Reversion
    • Direction: Both
    • Indicators: Bollinger
    • Stops: Yes
    • Complexity: Intermediate
    • Timeframe: Short-term
    • Seasonality: No
    • Neural Networks: No
    • Divergence: No
    • Risk Level: Medium
using System;
using System.Collections.Generic;

using Ecng.Common;

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

namespace StockSharp.Samples.Strategies;

/// <summary>
/// Bollinger Bands width mean reversion.
/// Enters when the band width is beyond its average by a standard deviation multiplier and starts
/// turning back toward the average: long on an extreme contraction, short on an extreme expansion.
/// Exits when the width returns to its average or the ATR stop is hit.
/// </summary>
public class BollingerWidthMeanReversionStrategy : Strategy
{
	private readonly StrategyParam<int> _bollingerLength;
	private readonly StrategyParam<decimal> _bollingerDeviation;
	private readonly StrategyParam<int> _widthLookbackPeriod;
	private readonly StrategyParam<decimal> _widthDeviationMultiplier;
	private readonly StrategyParam<int> _atrPeriod;
	private readonly StrategyParam<decimal> _atrMultiplier;
	private readonly StrategyParam<DataType> _candleType;

	private SimpleMovingAverage _widthAverage;
	private StandardDeviation _widthStdDev;
	private decimal? _prevWidth;
	private decimal _stopPrice;

	/// <summary>
	/// Bollinger Bands period.
	/// </summary>
	public int BollingerLength
	{
		get => _bollingerLength.Value;
		set => _bollingerLength.Value = value;
	}

	/// <summary>
	/// Bollinger Bands deviation.
	/// </summary>
	public decimal BollingerDeviation
	{
		get => _bollingerDeviation.Value;
		set => _bollingerDeviation.Value = value;
	}

	/// <summary>
	/// Lookback period for width statistics.
	/// </summary>
	public int WidthLookbackPeriod
	{
		get => _widthLookbackPeriod.Value;
		set => _widthLookbackPeriod.Value = value;
	}

	/// <summary>
	/// Standard deviation multiplier for extreme width.
	/// </summary>
	public decimal WidthDeviationMultiplier
	{
		get => _widthDeviationMultiplier.Value;
		set => _widthDeviationMultiplier.Value = value;
	}

	/// <summary>
	/// ATR period for the stop.
	/// </summary>
	public int AtrPeriod
	{
		get => _atrPeriod.Value;
		set => _atrPeriod.Value = value;
	}

	/// <summary>
	/// Stop-loss distance in ATR multiples.
	/// </summary>
	public decimal AtrMultiplier
	{
		get => _atrMultiplier.Value;
		set => _atrMultiplier.Value = value;
	}

	/// <summary>
	/// Candle type.
	/// </summary>
	public DataType CandleType
	{
		get => _candleType.Value;
		set => _candleType.Value = value;
	}

	/// <summary>
	/// Initialize <see cref="BollingerWidthMeanReversionStrategy"/>.
	/// </summary>
	public BollingerWidthMeanReversionStrategy()
	{
		_bollingerLength = Param(nameof(BollingerLength), 20)
			.SetGreaterThanZero()
			.SetDisplay("Bollinger Length", "Period of Bollinger Bands", "Indicators");

		_bollingerDeviation = Param(nameof(BollingerDeviation), 2.0m)
			.SetGreaterThanZero()
			.SetDisplay("Bollinger Deviation", "Standard deviations for Bollinger Bands", "Indicators");

		_widthLookbackPeriod = Param(nameof(WidthLookbackPeriod), 20)
			.SetGreaterThanZero()
			.SetDisplay("Width Lookback", "Period for width statistics", "Strategy");

		_widthDeviationMultiplier = Param(nameof(WidthDeviationMultiplier), 2.0m)
			.SetGreaterThanZero()
			.SetDisplay("Width Deviation Multiplier", "Standard deviation multiplier for extreme width", "Strategy");

		_atrPeriod = Param(nameof(AtrPeriod), 14)
			.SetGreaterThanZero()
			.SetDisplay("ATR Period", "ATR period for the stop", "Risk Management");

		_atrMultiplier = Param(nameof(AtrMultiplier), 2.0m)
			.SetNotNegative()
			.SetDisplay("ATR Multiplier", "Stop-loss distance in ATR multiples", "Risk Management");

		_candleType = Param(nameof(CandleType), TimeSpan.FromMinutes(5).TimeFrame())
			.SetDisplay("Candle Type", "Type of candles to use", "General");
	}

	/// <inheritdoc />
	public override IEnumerable<(Security sec, DataType dt)> GetWorkingSecurities()
	{
		return [(Security, CandleType)];
	}

	/// <inheritdoc />
	protected override void OnReseted()
	{
		base.OnReseted();
		_widthAverage = null;
		_widthStdDev = null;
		_prevWidth = null;
		_stopPrice = 0m;
	}

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

		var bollinger = new BollingerBands { Length = BollingerLength, Width = BollingerDeviation };
		var atr = new AverageTrueRange { Length = AtrPeriod };
		_widthAverage = new SimpleMovingAverage { Length = WidthLookbackPeriod };
		_widthStdDev = new StandardDeviation { Length = WidthLookbackPeriod };

		var subscription = SubscribeCandles(CandleType);
		subscription
			.BindEx(bollinger, atr, ProcessCandle)
			.Start();

		var area = CreateChartArea();
		if (area != null)
		{
			DrawCandles(area, subscription);
			DrawIndicator(area, bollinger);
			DrawOwnTrades(area);
		}
	}

	private void ProcessCandle(ICandleMessage candle, IIndicatorValue bollingerValue, IIndicatorValue atrValue)
	{
		if (candle.State != CandleStates.Finished)
			return;

		if (!bollingerValue.IsFormed || !atrValue.IsFormed)
			return;

		var bb = (BollingerBandsValue)bollingerValue;
		if (bb.UpBand is not decimal upper || bb.LowBand is not decimal lower)
			return;

		var atr = atrValue.ToDecimal();
		var width = upper - lower;
		var avgWidth = _widthAverage.Process(width, candle.ServerTime, true).ToDecimal();
		var stdWidth = _widthStdDev.Process(width, candle.ServerTime, true).ToDecimal();

		var prevWidth = _prevWidth;
		_prevWidth = width;

		if (!_widthAverage.IsFormed || !_widthStdDev.IsFormed || prevWidth is not decimal prev)
			return;

		if (!IsFormedAndOnlineAndAllowTrading())
			return;

		if (CheckStop(candle))
			return;

		var close = candle.ClosePrice;
		var stopDistance = AtrMultiplier * atr;

		// Extreme reading that has started to turn back toward the average.
		if (width < avgWidth - WidthDeviationMultiplier * stdWidth && width > prev && Position <= 0)
		{
			BuyMarket(Volume + Math.Abs(Position));
			_stopPrice = stopDistance > 0 ? close - stopDistance : 0m;
		}
		else if (width > avgWidth + WidthDeviationMultiplier * stdWidth && width < prev && Position >= 0)
		{
			SellMarket(Volume + Math.Abs(Position));
			_stopPrice = stopDistance > 0 ? close + stopDistance : 0m;
		}
		else if ((Position > 0 && width >= avgWidth) || (Position < 0 && width <= avgWidth))
		{
			ExitPosition();
		}
	}

	private bool CheckStop(ICandleMessage candle)
	{
		if (_stopPrice == 0m)
			return false;

		if ((Position > 0 && candle.LowPrice <= _stopPrice) || (Position < 0 && candle.HighPrice >= _stopPrice))
		{
			ExitPosition();
			return true;
		}

		return false;
	}

	private void ExitPosition()
	{
		if (Position > 0)
			SellMarket(Position);
		else if (Position < 0)
			BuyMarket(-Position);

		_stopPrice = 0m;
	}
}