Measures of Dispersion

Mean Deviation

The average of the absolute differences between each data value and the mean.

Variance and Standard Deviation

Variance measures the average squared deviation from the mean:

$$\sigma^2 = \frac{1}{n}\sum_{i=1}^{n}(x_i - \bar{x})^2$$

The standard deviation ($\sigma$) is the square root of the variance, bringing the measure back to the original units.