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20#
发表于 2012-3-22 16:50
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Closing prices for a commodity were 21.4 on Monday, 22.2 on Tuesday, 21.8 on Wednesday, 22.4 on Thursday, and 23.2 on Friday. The five-day standard deviation is 0.7 and the 30-day standard deviation is 1.0. On Friday, five-day Bollinger bands using two standard deviations are closest to:
Bollinger bands are drawn a chosen number of standard deviations above and below a moving average, where the moving average and the standard deviation are calculated using the same number of periods. The 5-day moving average is (21.4 + 22.2 + 21.8 + 22.4 + 23.2) / 5 = 22.2. Using two 5-day standard deviations, the upper band on Friday is 22.2 + 2(0.7) = 23.6 and the lower band is 22.2 − 2(0.7) = 20.8. |
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