Developed by John Bollinger, Bollinger Bands® are volatility bands placed above and below a moving average. Volatility is based on the standard deviation, which changes as volatility increases and decreases. The bands automatically widen when volatility increases and narrow when volatility decreases. This dynamic nature of Bollinger Bands also means they can be used on different securities with the standard settings. For signals, Bollinger Bands can be used to identify M-Tops and W-Bottoms or to determine the strength of the trend. Signals derived from narrowing BandWidth are discussed in the ChartSchool article on BandWidth.
Bollinger Bands consist of a middle band with two outer bands. The middle band is a simple moving average that is usually set at 20 periods. A simple moving average is used because the standard deviation formula also uses a simple moving average. The look-back period for the standard deviation is the same as for the simple moving average. The outer bands are usually set 2 standard deviations above and below the middle band.
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Settings in the chart
Settings in Strategies
Since the Bollinger Bands indicator consists of two separate components (Bollinger Bands High, Bollinger Bands Low) each of which has its own parameters and values, in Strategy Builder the Alligator is also divided into two indicators:
- Bollinger Bands High
- Bollinger Bands Low
All indicators can be used either together or separately with other indicators.