Over the years numerous technical indicators have been developed to describe performance, as well as to predict future price movements. In this section we introduce five of the most useful indicators and explain how they are calculated.

Sometimes prices appear to remain in a range for extended periods of time. A good way to describe this situation is to define a moving range around the prices. Some people use an upper boundary and a lower boundary to define the range; the upper boundary is calculated as a moving average of a chosen period plus 5% of the price, and the lower boundary is the moving average minus 5%. These boundaries have the drawback of being too narrow to accommodate price levels when volatility is high and too wide when volatility is low. A better solution, recommended by John Bollinger, defines the upper boundary as a chosen moving average plus twice the corresponding standard deviation, with the lower boundary as the moving average minus twice the standard deviation. The method is described below:

The Bollinger Band includes 3 lines: the upper band, lower band, and the centerline. The centerline is simply the moving average, and the upper and lower bands are, respectively, the center line plus/minus twice the standard deviation. For a p-period Bollinger band:

Center Line = p-period moving average

Upper Band = Center Line + 2 x StdDev

Lower Band = Center Line - 2 x StdDev

Figure 5. Bollinger Band

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