# Standard Deviation

The standard deviation is a statistic defined as the square root of the variance that measures how spread out a set of data is.

Standard deviation is a high school-level concept that would be first encountered in a probability and statistics course. It is an Advanced Placement Statistics topic and is listed in the California State Standards for Probability and Statistics.

### Prerequisites

Arithmetic Mean: | Arithmetic mean is a synonym for average, i.e., the sum of all values in a list divided by the number of values present. |

Variance: | In statistics, variance is the measure of the expected deviation from the mean. The square root of the variance is the standard deviation. |