Sulfur in coal seams

A study was made to compare the sulfur content of the five major coal (labeled S1 to S5, respectively) seams in a particular region.

Variables.

1. SULFUR: Sulfur content
2. SEAM: Coal seam label

Source. Milton, J.S. and Arnold, J.C. (1995). Introduction to probability and statistics, McGraw Hill International Editions.