George, Victor
Routledge & Kegan Paul, 1985
Buku Teks
Rosen, Paul L.
University of Illinois Press, 1972
Buku Teks
Spicker, Paul
Prentice-Hall, 1995
Buku Teks
Berreman, Gerald D., author
New York Cornell University 1956,
Buku Teks
Mishan, F.I.
Praeger, 1972
Buku Teks