Part III. Two-Variable Graphs

It is natural to study the relationship between two variables. If we examine two quantitative variables, we might wonder if they are associated or correlated; that is, do they vary together? Or, put another way, does one become larger as the other grows in size? Or perhaps just the opposite: does one grow larger as the other becomes smaller? Is there some other kind of relationship? Or perhaps no relationship at all? Two-variable graphs enable us to address such questions as these.