PCA of prominent significant wavenumbers. Plots produced after application of PCA to the panel of significant wavenumbers. (A) Scree plot showing the number of components to retain explaining at least 5% of the variation. The first 3 components explain 95% variance. Scatterplots of the loadings of each cancer (C) and normal (N) sputum spectrum on: (B) components 1 (PC1) and 2 (PC2); (C) components 1 and 3 (PC3); (D) components 2 and 3.