N n e β(∆ n+1→n +∆A) n+1 where N n and N n+1 respectively are the number of statistically independent samples in states n and n + 1, and ∆ n→n+1 = -∆ n+1→n are the Hamiltonian differences between n and n + 1. BAR is more efficient than EXP and minimizes the free energy uncertainty . Multistate Bennett acceptance ratio (MBAR) is an extension of BAR that takes in consideration the degree of configuration space overlap between a given state and all other states in the transformation, while BAR only uses the information of neighboring states. MBAR and BAR perform similarly when the spacing between the intermediate states is moderate, but MBAR is the most wellperforming free energy estimator .