A number of approaches have been devised for the calculation of sample size for microarray experiments, but to date little consensus exists [126] [127] [128] [129] . Hence, best practices in the fi eld consist of the utilization of independent sets of samples for the purpose of validating candidate signatures. Thus, the robustness of the signature identifi ed will rely on a statistically signifi cant association between the predicted and true phenotypic class in the fi rst and the second test sets.