Forex Trading - Bollinger Bands

Bollinger Bands are a tool of technical analysis which was invented by John Bollinger in the 1980s. Having evolved from the concept of trading bands, Bollinger Bands are an indicator that allows users to compare volatility and relative price levels over a period time. Basically, this tool provides a relative definition of high and low. By definition prices are high at the upper band and low at the lower band. This definition can aid in rigorous pattern recognition and is useful in comparing price action to the action of indicators to arrive at systematic trading decisions. When the market is calm, the Bollinger Band lines get closer together and when the market was changing Bollinger Band line expand. The indicator consists of three bands designed to encompass the majority of a security's price action:

1. A simple moving average in the middle
2. An upper band (SMA plus 2 standard deviations)
3. A lower band (SMA minus 2 standard deviations)



Standard deviation is a statistical unit of measure that provides a good assessment of a price plot's volatility. Using the standard deviation ensures that the bands will react quickly to price movements and reflect periods of high and low volatility. Sharp price increases (or decreases), and hence volatility, will lead to a widening of the bands.

For easier understanding, see the following chart: when the price was calm, Bollinger Band lines were close to one another, but when the price jumped up, Bollinger Band lines are spread. The same would happen if the price fell.



Calculation

Upper = Average + 2*SD = X + 2*σ
Middle = Average = X
Lower = Average - 2*SD = X - 2*σ

Bollinger Bounce

The first thing you should know about Bollinger Band is that prices strive to return to the center of the Bollinger Bands. On the following chart you can see that the price has returned back towards the middle of Bollinger Bands.



What you just saw was a classic Bollinger Bounce. The reason why this “bounce” occurs is that Bollinger Band lines act like a level of support and resistance. The larger time period that you observe in the graph (H1, H4, D1), the stronger the Bollinger Bands get. Most traders developed systems that rely on the “jumps”. This strategy is best used when the market is in the range (ranging market) and while there is no clear trend.