which establishes our sign convention. Of all the functionals that we tested, only the ones lacking dispersion corrections afford mean absolute errors (MAEs) larger than 1 kcal/mol, with the exception of B97+D3 and B97+MBD. In the absence of any dispersion correction, average signed errors [Fig. ] range up to 3.5 kcal/mol (for BLYP), which is quite large considering that the average CCSD(T)/CBS interaction energy for the S66 complexes is only 4.8 kcal/mol. It is interesting that all of the dispersion-inclusive approaches overestimate the interaction energies. Unlike the underbinding observed in the absence of dispersion corrections, which is entirely predictable, overbinding by dispersion-inclusive approaches would not seem to be built in by design but emerges nonetheless. The effect is rather small, however. Setting aside B97+D3 and B97+MBD, the differences in error statistics from one functional to the next are smaller than the statistical errors with respect to the reference values, and in that sense the accuracy of these dispersion-inclusive hybrid and meta-GGA functionals is statistically indistinguishable. Consistent with other statistical assessments, these results demonstrate unequivocally that DFT provides interaction energies of sub-kcal/mol accuracy for small vdW dimers.