The Variance

The variance  (denoted S²) is simply the square of the SD.

$$S^2= \frac{\sum \vert X_i-\overline{X}\vert^2}{n-1}$$ (3.3)

Some statistical computing packages (Excel included) report both the variance and the SD when computing summary statistics. Some textbooks also emphasize the variance along with the SD. In this text, we will always refer to the SD when discussing methodology and formulas.