Measures of central dispersion show how "spread out" the elements of a data set are from the mean. Three of the most commonly used measures of central dispersion include the following:

Range

Variance

Standard deviation

## Range

The *range* of a data set is the difference between the largest value and the smallest value. You compute it the same way for both samples and populations.

## Variance

You can think of the variance as the average *squared* difference between the elements of a data set and the mean. The formulas for computing a sample variance and a population variance are slightly different.

Here is the formula for computing sample variance:

And here is the formula for computing population variance:

## Standard deviation

The standard deviation is simply the square root of the variance. It's more commonly used as a measure of dispersion than the variance because it's measured in the same units as the elements of the data set, whereas the variance is measured in *squared *units.