The average overlap (green column) is 0.54 indicating that the atomic attributions are largely correct for a majority of the molecules. For comparison, a null-model attribution vector, where each atom is assigned the value logP/N where logP is the predicted value and N is the number of non-H atoms, results in an average overlap of 0.32 (Figure ). Figure and shows plots of the atomic attributions and the ground truth contributions, respectively, for a molecule (1) with an overlap (0.66) close to the average. Both plots show positive contributions from the phenyl rings, but the rest of the atoms in the molecule do not appear to contribute significantly to the predicted logP value, in contrast to the ground truth. Never-the-less the logP value is predicted to within 0.3 units. One possible reason is that when using a FP radius of two, the removal of an atom results in the removal of a relatively large chunk of the molecule, while the associated change in logP is ascribed to a single atom. For example, removing the carbonyl C atom in the pyrrolidone ring actually removes the entire moiety plus part of the substituents (Figure ) and the combined atomic logP contributions of these atoms, which is roughly zero, is assigned to that atom. To quantify this effect we compute the sum of the logP contributions for each of the ten fragments and assign it to the carbonyl C and