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Bollinger Bands is a technical analysis tool invented by John Bollinger in the 1980s as well as a term trademarked by him in 2011. Having evolved from the concept of trading bands, Bollinger Bands and the related indicators %''b'' and ''bandwidth'' can be used to measure the "highness" or "lowness" of the price relative to previous trades. Bollinger Bands are a volatility indicator similar to the Keltner channel. Bollinger Bands consist of: * an ''N''-period moving average (MA) * an upper band at ''K'' times an ''N''-period standard deviation above the moving average (MA + ''Kσ'') * a lower band at ''K'' times an ''N''-period standard deviation below the moving average (MA − ''Kσ'') Typical values for ''N'' and ''K'' are 20 and 2, respectively. The default choice for the average is a simple moving average, but other types of averages can be employed as needed. Exponential moving averages is a common second choice. Usually the same period is used for both the middle band and the calculation of standard deviation.〔Since Bollinger Bands use the population method of calculating standard deviation, the proper divisor for the sigma calculation is ''n'', not ''n'' − 1.〕 == Purpose == The purpose of Bollinger Bands is to provide 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.〔() second paragraph, center column〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bollinger Bands」の詳細全文を読む スポンサード リンク
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