The standard deviation is the square root of the variance for a distribution. Like the variance, it is a measure of dispersion about the mean and is useful for describing the “average” deviation. See the description for the variance in the next section.
For example, you can calculate the standard deviation of the values 1, 3, 6, 7, and 9 by finding the square root of the variance that is calculated in the variance example that follows.
The standard deviation, denoted as s, is calculated from the variance as follows:
