Standardizing Activity Measurements: Experimental activity measurements such as K d , K i , and IC 50 can vary numerically by several orders of magnitude. To address this variability and provide a uniform scale for comparison, we introduced a standardization method where the strength of a protein-ligand interaction is characterized by the value of pX (pChEMBL), calculated using the formula: pX = -log 10 (X), where X represents the numerical value of IC 50 , K i , or K d expressed in molar concentration .