Comparison of External Indices.

D indicates the dataset containing N data objects, and its a priori partition with l categories is . The result obtained from clustering is , where k is the number of clusters. SS indicates that both objects belong to the same cluster of C and to the same group of partitions P; SD indicates points that belong to the same cluster of C and to different groups of P; DS indicates points that belong to different clusters of C and to the same group of P; and DD indicates points that belong to different clusters of C and to different groups of P.