Shohei Hido Yuta Tsuboi Hisashi Kashima Masashi Sugiyama Takafumi Kanamori Inlier-Based Outlier Detection via Direct Density Ratio Estimation. 223-232 2008 ICDM http://dx.doi.org/10.1109/ICDM.2008.49 conf/icdm/2008 db/conf/icdm/icdm2008.html#HidoTKSK08