# Standard deviation

### From Conservapedia

This article/section deals with mathematical concepts appropriate for a student in late high school or early university. |

**Standard deviation** is a measure in statistics of the dispersion of a set of values (represented as *X*). It is defined as the square root of the variance of these values, where variance is defined as

where the expected value of *X* is E(*X*).

Thus the standard deviation is

The formula for standard deviation must not be confused with the formula

(where is the sample mean).

which is the formula for a point estimate of the true standard deviation from a sample size of *n*. As such this statistical estimator itself has a variance which, as the formula indicates, decreases as the sample size increases.