1. A computer-implemented method for generating a reference set via clustering, comprising the steps of: obtaining a collection of unclassified documents; grouping the unclassified documents into clusters; selecting n-documents from each cluster, comprising: building a hierarchical tree of the clusters; and traversing the hierarchical tree to identify the n-documents, wherein one of the n-documents from each cluster is located closest to a center of that cluster; combining the selected n-documents as reference set candidates assigning a classification code to each of the reference set candidates; and grouping two or more of the reference set candidates as a reference set of classified documents, wherein the steps are performed by a suitably programmed computer.