Definition

The standard deviation is a measure of the dispersion. The sample standard deviation is the square root of the sample variance. The sample variance is calculated as the sum of the squared deviations of the individual observations in the sample of data from the sample average divided by the total number of observations in the sample minus one. In a normal distribution, about 68 percent of the observations lie within one standard deviation above and below the average and about 95 percent of the observations lie within two standard deviations above and below the average.

Source

• In the Matter of Connect America Fund, at 32 n.123.