For the score plot group comparisons, the relative score contribution for variable j is the difference between the average contribution in group B and the average contribution in group A:
where
T*i = the ith row of the score matrix with columns corresponding to the dimensions shown in the score plot.
A = the set of observations in group A
B = the set of observations in group B
na = the number of observations in group A
nb = the number of observations in group B.