Bivariate descriptive displays or plots are designed to reveal the relationship between two variables.  As was the case when examining single variables, there are several basic characteristics of the relationship between two variables that are of interest.  These include:

• the form of the relationship

• the strength of the relationship, and 

• the dependence of the relationship on external (to the two variables being examined) circumstances.

Bivariate plots provide the means for characterizing pair-wise relationships between variables.  Some simple extensions to such plots, such as presenting multiple bivariate plots in a single diagram, or labeling the points in a plot, allow simultaneous relationships among a number of variables to be viewed.

Bivariate plots (and variations)

• scatter plot examples

Readings: 

Owen (The R Guide):  Ch. 5; Kuhnert & Venebles (An Introduction...):  p. 80-85; Cleveland (Visualizing Data):  ch. 3;