This is further evidence that the three NP metrics can considered as independent measures of Clinical compound quality. Consistent with their defined make-up, PNPs contain on average two more NP fragments than NonPNPs (illustrated for post-2008 Clinical compounds in Table ; see Table .2 for a full summary of the physical properties examined). Accordingly, PNPs and NonPNPs have markedly different ring counts, both aromatic and aliphatic. The number of heteroaromatic rings and aromatic nitrogen atoms are more than doubled in PNPs versus NonPNPs, while there are fewer carboaromatic rings in PNPs (Table ). Aliphatic ring counts are also significantly increased in PNPs versus NonPNPs.