Figure 1. Ligand, system and observational bias.
Ligand and system bias together determine the functional selectivity
(see Terminology subsection for definitions). Each type of bias is
measured relative to a reference. Observational bias is not of
biological origin, but a consequence of assay sensitivity/non-linearity
and the parameters chosen in the experimental setup (which may or may
not be appropriate for the intended measurements and efficacies of
ligands).