Shall I compare thee to a summer's day?
William Shakespeare (Sonnet 18)
Chapter 10 covers making comparisons using graphics, complementing more formal statistical methods of comparison.
Many scientific studies are carried out in a two-group design using a treated group and a control group. The groups are then commonly compared on the basis of the difference between their two means, using a two-sample t-test, assuming that the samples are drawn from normal distributions with equal variances. There may be other interesting features in the data, which cannot be formally compared because the sample sizes are too small. This should not stop us from looking at the data, and ...