Plot boxplots for FSIQ, PIQ, and the paired difference between the two: while the spread (error bars) for FSIQ and PIQ are very large, there is a systematic (common) effect due to the subjects. This effect is cancelled out in the difference and the spread of the difference (“paired” by subject) is much smaller than the spread of the individual measures.
Python source code: plot_paired_boxplots.py
import pandas
import matplotlib.pyplot as plt
data = pandas.read_csv('brain_size.csv', sep=';', na_values='.')
# Box plot of FSIQ and PIQ (different measures od IQ)
plt.figure(figsize=(4, 3))
data.boxplot(column=['FSIQ', 'PIQ'])
# Boxplot of the difference
plt.figure(figsize=(4, 3))
plt.boxplot(data['FSIQ'] - data['PIQ'])
plt.xticks((1, ), ('FSIQ - PIQ', ))
plt.show()
Total running time of the example: 2.06 seconds ( 0 minutes 2.06 seconds)