Heng Zhao Jimin Liang Haihong Hu Clustering Validity Based on the Improved Hubert Gamma Statistic and the Separation of Clusters. 539-543 2006 conf/icicic/2006 ICICIC (2) http://doi.ieeecomputersociety.org/10.1109/ICICIC.2006.250 db/conf/icicic/icicic2006-2.html#ZhaoLH06