Siagian, Sondang P., author
Bumi Aksara, 2004
Buku Teks
Robbins, Lionel Robbins, Baron, 1898-1984, editor
Macmilan Co., 1936
Buku Teks
Klatt, Edward C., author
Saunders Elsevier, 2010
Buku Referensi
Anthony Robbins
imon & Schuster, 1988
Buku Teks
Robbins, Harold,
New English Library, 1982
Buku Teks