for each target property. This drop is most pronounced for the A 2A R pKi (mean R 2 from 0.70 to 0.46). This may be due to the smaller diversity in the A 2A R receptor set, compared to the PK set. Another possible cause is the higher initial performance and therefore more potential to decrease. Hence, there is less difference between the random split and the cluster split for the PK dataset than the A 2A R dataset.