Sometimes there are additional variables that were not included in the PCA because
they are a combination of the other variables. It can still be useful to add these variables
to the plot as additional axes to help interpretation.
The plot shows the additional axis named rank (colored green in the plot).
Due to its poor representation, only 25% of variation in the original variable is
explained by the first two principal components, we will not pursue interpreting it
any further. This is not surprising, given it is a weighted average of the other
scores that have varying degrees of correlation between them.