Interpret Parallel Plots

To help you interpret parallel plots, compare the parallel plot with a scatterplot. In each of the following figures, the parallel plot appears on the left side of the figure, and the scatterplot appears on the right side of the figure.

Strong Positive Correlation

The following relationship shows a strong positive correlation. Notice the coherence of the lines in the parallel plot.

Figure 7.6 Strong Positive Correlation 

Strong Negative Correlation

A strong negative correlation, by contrast, shows a narrow neck in the parallel plot.

Figure 7.7 Strong Negative Correlation 

Collinear Groups

Consider a case that encompasses both situations: two groups, both strongly collinear. One group has a positive slope, and the other group has a negative slope. In Figure 7.8, the positively sloped group is highlighted.

Figure 7.8 Collinear Groups: Parallel Plot and Scatterplot 

Single Outlier

In the case of a single outlier, the parallel plot shows a general coherence among the lines, with a noticeable exception.

Figure 7.9 Single Outlier: Parallel Plot and Scatterplot 

For more examples, see Additional Examples of the Parallel Plot Platform.