Variance and standard deviation

Statistical Thinking in Python (Part 1)

Justin Bois

Teaching Professor at the California Institute of Technology

2008 US swing state election results

¹ Data retrieved from Data.gov (https://www.data.gov/)

Variance

• The mean squared distance of the data from their mean
• Informally, a measure of the spread of data

2008 Florida election results

¹ Data retrieved from Data.gov (https://www.data.gov/)

2008 Florida election results

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

¹ Data retrieved from Data.gov (https://www.data.gov/)

Computing the variance

np.var(dem_share_FL)
147.44278618846064

Computing the standard deviation

np.std(dem_share_FL)

12.142602117687158

np.sqrt(np.var(dem_share_FL))

12.142602117687158

2008 Florida election results

¹ Data retrieved from Data.gov (https://www.data.gov/)

Let's practice!

Statistical Thinking in Python (Part 1)