7Robertson J. Likert-type scales, statistical meth- ods, and effect sizes[J]. Communications of the ACM, 2012,55(5) :6-7.
8Johnson R A , Wiehern D W. Applied Multivariate Statistical Analysis[M]. Upper Saddle River: Pren- tice Hall, 2007.
9von Luxburg U. A tutorial on spectral clustering [J]. Statistics and Computing, 2007, 17 (4) : 395- 416.
10Cai D, He X, Han J. Document clustering using lo- cality preserving indexing[J]. IEEE Transactions on Knowledge and Data Engineering, 2005, 17 (12): 1624-1637.
