editor, Poltak Partogi Nainggolan
Pusat Pengkajian dan Pengolahan Data dan Informasi Sekjen DPR RI, 2009
Buku Teks SO
Universitas Indonesia, 1985
UI - Skripsi Membership
Reader's Digest Association.
Reader's Digest Association, 1968
Buku Referensi
Wilson, Lindsay
McGraw-Hill , 1975
Buku Teks SO
Woolford, Donald Mark
University of Queensland Press, 1976
Buku Teks SO