The spreadsheet above shows an example for a 10-period standard deviation using QQQQ data. Notice that the 10-period average is calculated after the 10th period and this average is applied to all 10 periods. Building a running standard deviation with this formula would be quite intensive. Excel has an easier way with the STDEVP formula. The table below shows the 10-period standard deviation using this formula.

The calculation of the Standard Deviation can be accomplished in six steps. For example, to calculate a 10-period standard deviation.

<P>Standard Deviation - Definition for Standard Deviation from Morningstar - This statistical measurement of dispersion about an average, depicts how widely a mutual fund's returns varied over a certain period of time.</P>