Kostka, Stefan
McGraw-Hill , 2000
Buku Teks
Ewen, David, author
Prentice Hall, 1968
Buku Referensi
Thwaite, Anthony, author
Heineman, 1984
Buku Teks
Proctor, George A.
University of Toronto Press, 1980
Buku Teks
edited by Jack A. Goldstone, Ted Robert Gurr, Farrokh Moshiri
Westview Press, 1991
Buku Teks