Hands-On Data Science and Python Machine Learning

Measuring variance

We usually refer to variance as sigma squared, and you'll find out why momentarily, but for now, just know that variance is the average of the squared differences from the mean.

1. To compute the variance of a dataset, you first figure out the mean of it. Let's say I have some data that could represent anything. Let's say maximum number of people that were standing in line for a given hour. In the first hour, I observed 1 person standing in line, then 4, then 5, then 4, then 8.
2. The first step in computing the variance is just to find the mean, or the average, of that data. I add them all, divide the sum by the number of data points, and that comes out to 4.4 which is the average number of people standing in line (1+4+5+4+8)/5 ...