The differences in Figure reflect inherent biases. For example, predicted probes have almost double the number of GPCRs 52 but, compared to predicted probes, proportionally fewer kinases and epigenetic regulators. This is likely due to the challenges of optimising single-target selective ligands within these target families. However, probes with intra-family selectivity can also be experimentally useful but run the risk of being rejected by quality scoring weighted towards singletarget selectivity.