Hands-On Data Analysis with Pandas

Variance

Just from the definition of the range, we can see why that wouldn't always be the best way to measure the spread of our data. It gives us upper and lower bounds on what we have in the data, however, if we have any outliers in our data, the range will be rendered useless.

Another problem with the range is that it doesn't tell us how the data is dispersed around its center; it really only tells us how dispersed the entire dataset is. Enter the variance, which describes how far apart observations are spread out from their average value (the mean). The population variance is denoted as sigma-squared (σ²), and the sample variance is written as (s²).

The variance is calculated as the average squared distance from the mean. The distances ...