Matondang E Siburian Graduate School of Economics, Waseda University. Indonesian Directorate of Taxes   Kantor Pusat Direktorat Jenderal Pajak Jalan, Jend. Gatot Subroto No.40-42 Gedung B Lt.15 Jakarta, Jakarta 12190 Indonesia   mes1701@fuji.waseda.jp             JEL Areas: H : Public Economics C0 : Mathematical and Quantitative Methods: General