FIG. 5.

Sources of variation visualized by PCA. PCA was performed on the LEL matrix of all 1060 chemicals. Plotting symbols annotate chemicals into activity categories: mortality only (empty triangle), mortality plus specific endpoint(s) (black triangle with red filling), specific endpoint(s) only (red solid circle), or inactive (hollow red circle). The points are scaled according to how many specific endpoint LELs are associated with each chemical. Abbreviations: LEL, lowest effect level; PCA, principal components analysis.