where the vertical bars on each side of the subset is the cardinality or number of elements in the subset. We find that the relative success of high P(active) building blocks correlates with these building blocks being compatible with a broad range of partners in both positions. We observe a monotonically increasing relationship between P(active) and number of compatible partners for all building block pairs (Figure ). P(active) tells us how successful a building block is when it is placed in a certain position, but tells us nothing about the behavior at other positions that may lead to the success (or lack thereof) at one position. Hypothetically, a building block could have a high P(active) value but only form active compounds with a very limited selection of partners in one of the other positions. To illustrate this possibility, all active molecules that contain bb x in p 3 only occur if one or a few specific building blocks are present in p 2 , so the only variation between these active molecules is the identity of the building block in p 1 . Since we find the least sensitivity to molecule activity in p 1 (Figure ), this is a realistic hypothesis to rule out. We find that this possibility is not the case. On the contrary, we see that building blocks which are successful in one position are compatible with a broader diversity of building blocks in all other positions. We can therefore be more confident that a compound containing an untested building block is active if it contains a high P(active) building block in any position (Figure , Table ). The observation that high P(active) building blocks are compatible with more partners also suggests that building block level data could be useful for a predictive model of molecule activity.