Principal component analysis (PCA) of gene expression data after 24 h of chemical stimulation. To investigate consistency of gene expression data from evaluated platforms, samples from Figure 5 were instead colored according to chemical stimulation. Subplots (A-D) illustrates PCA plots constructed from gene expression data obtained on the various platforms. A) Affymetrix®, 48 stimulations. B) nCounter®, 42 stimulations. C) BioMark HD, 39 stimulations. D) OpenArray®, 36 stimulations.