Allan, Barbara, author
Facet Publishing, 2004
Buku Teks
Lockyer, Keith, author
Prentice-Hall, 1996
Buku Teks
Lock, Dennis, author
Gower, 2003
Buku Teks
Kendrick, Tom, author
American Management Association, 2004
eBooks
Russell, Doug, author
Amacom, 2011
Buku Teks