Fig. 4

Boxplots of the distribution of features values obtained on the DB1 for all considered levels of fractionation (0, 1, 2 and 3). Top row—the selected feature subset \({\varXi }^{*}\); bottom row— the rejected feature subset. Red crosses mark outliers. All selected features have almost non-overlapping boxplots. This fact illustrates the ability of each feature in separating the classes. Results of Spearman correlation \(\rho\) between each feature and the classes of fractionation is shown