Gormley, William T., author
CQ Press, 2004
Buku Teks
Osborner, David, author
Pustaka Binaman Pressindo, 1996
Buku Teks
edited by Francis E. Rourke
Little, Brown, 1978
Buku Teks
Leiserson, Avery
The University of Chicago Press, 1942
Buku Teks
Sage Publications, 1980
Buku Teks