Bone, Hugh A., author
University of Washington Press, 1958
Buku Teks
Caramani, Daniele, author
Camberidge University Press , 2004
Buku Teks
Jupp, James
London Melbourne University Press 1964
Buku Teks
Sorauf
Little, Brown and Company, 1980
Buku Teks
Burns, James McGregor, author
Prentice-Hall, 1963
Buku Teks