Redfern, Darren
Springer, 1998
Buku Teks
American Enterprise Institute for Public Policy Research, 1977
Buku Teks
Spencer, Donald D.
Charles E. Merrill, 1982
Buku Teks SO
Orilia, Lawrence S.
McGraw-Hill, 1982
Buku Teks SO
Cashman, Thomas J.
Anaheim Publishing, 1970
Buku Teks