Griffith, Martin
Routledge, 2002
Buku Teks
Frankel, Joseph
Oxford University Press, 1964
Buku Teks SO
edited by Beth A. Simmons and Richard H. Steinberg
Cambridge University Press, 2006
Buku Teks SO
Dilenschneider, Robert L.
American Management Association, 2010
eBooks
edited by Philip Lesly
Prentice-Hall, 1955
Buku Teks SO