“…Fiftythree compounds were taken in the calibration set (1 -2, 4 -7, 9 -13, 15, 18 -23, 25 -29, 31 -35, 37 -38, 40 -44, 46 -53, 55 -59, 61 -62, 65 -67) and fifteen compounds (3,8,14,16,17,24,30,36,39,45, 54, 60, 63, 64 and 68) were taken in the test set; four molecules of the test set are inactive, the remaining eleven have different levels of activity. Figure 2 represents the objects selected for the external test set (labelled with their index); Figure 2A shows the dispersion of these objects in the space of their structural variations (first two PCs of the autoscaled descriptors, representing 53.1% of total variance); the histogram of Figure 2B shows the same objects on the base of the value of their biological activity.…”