The second area is the allocation of sampling time. For a free energy calculation using information from two states, Bennett noted that the equal allocation of sampling time between states is at worst half-optimal. This is because the allocation of 1 hour of sampling to each state (2 hours total sampling) cannot yield a worse estimate than the optimal allocation of a total of 1 hour of sampling between both states, given that the variance of the estimate decreases monotonically with the number of samples from each state. However, an absolute binding free energy calculation uses samples from many (N ) states. The lower bound on the estimation efficiency with equal sampling time then falls to 1/N of the optimal allocation. Therefore large efficiency improvements may be made by the optimal allocation of sampling time when few states have a much higher computational cost per independent sample.