Strong outliers are identified from scores and Hotelling’s T2 range plots. The latter is a multivariate generalization of Student’s t-test, providing a check for observation adhering to multivariate normality . When used in conjunction with a scores plot, the Hotelling’s T2 defines the normality area corresponding to 95% confidence in this study. Inspecting the scores and Hotelling’s T2 range plots for the calculated four PC models (Figure 1A,B and Figure S2), no strong outliers were observed. The moderate outliers, on the other hand, are identified by inspecting the model residuals (X-variation that was not captured by the PC model). The detection tool for the moderate outliers is the distance to the model in X-space (DModX), with a maximum tolerable distance (Dcrit) .