MacKenthun, Kenneth M.
Lewis Publishers, 1998
Buku Teks
American Enterprise Institute for Public Policy Research, 1973
Buku Teks
Orr, Shannon K., author
CRC Press, 2014
Buku Teks
Floyd, Rita, author
Cambridge University Press, 2010
eBooks
Vig, Norman J.
CQ Press, 1984
Buku Teks