PCA loadings. The loadings from the PCA with the 725 most significant genes given in green. The actual number of significant genes is arbitrary, and corresponds to the number estimated from resampling of a Bridge-PLSR model. It is seen that the significant genes are scattered outside an elliptic shape centred at the origin. Genes with loadings of a large magnitude that vary little in the cross-validation are called significant. As neither of the components span the smoking history of the subjects, these features are irrelevant for classification.