From all the phase space, some zones of it are generally more important to the mean of the variable A than others. In particular, those that have the value of e − − β β E r → → i sufficiently high when compared to the rest of the energy spectra are the most relevant for the integral. Using this fact, the natural question to ask is: is it possible to choose, with more frequency, the states that are known to be more relevant to the integral? The answer is yes, using the importance sampling technique.