Mackie, Thomas T., author
Facts on File, 1982
Buku Referensi
Azim A. Nanji, editor
Gale Research, 1996
Buku Referensi
ed. by Howard S. Rowland
An Aspen publication , 1984
Buku Referensi
Dunne, Lavon J., author
McGraw-Hill , 2001
Buku Teks
Gordon Martel
Wiley Blackwell, 2010
Buku Teks