Experimental binding free energies (∆G expt ) for the first dataset were obtained from a combination of SPR, Alphascreen and Isothermal Titration Calorimetry (ITC) experiments , whereas those for the THQ dataset are derived from IC 50 values from FRET . These techniques are very different from one another and will necessarily introduce varying levels of uncertainty into the data they provide. The divergence in the origin of the measurements is typical of the sources of experimental data to which free energy calculations are typically compared. This alongside the lack of rigorously derived uncertainty estimates in the experimental data must be borne in mind when assessing protocol performance. .