Artikel Jurnal
Ranney, Austin, author
American Enterprise Institute, 1985
Buku Teks
Paul Hainsworth, Stephen McCloskey, editor
Tauris Publishers, 2000
Buku Teks
Sheldon, Charles H.
Westport Connneticat Greenwood Press , 1929
Buku Teks
H. Azhary, author
Ghalia Indonesia, 1982
Buku Teks