Fig. 9.

Graphs (a) and (c) show a two-dimensional plot of the first two principal component scores. Cluster 1 is represented in blue and cluster 2 in red; (b) and (d) show the first principal direction of variability. Blue = − 2 standard deviations (sd); green = − 1 sd; red = mean; cyan = + 1 sd; magenta = + 2 sd. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)