No rigorous criteria exist which relates the expected variance in the calculated free energy to the amount of sampling or overlap between states for a given system. As a result there are numerous other ways in which the reliability of FEP calculations are tested , such as calculating convergence of results with the amount of sampling/number of alchemical windows or computing overlap distributions and overlap matrices . The main way in which the variance in FEP calculation will be addressed in this work is through the use of ensembles of simulations. As described above for the TI estimator, the concept of ensemble simulations to obtain the expectation value of ∆G along with associated uncertainty will also be applied to FEP.