Walsh, William J., author
Skyhorse Publishing, 2014
Buku Teks
Levitin, Daniel J., author
Dutton, 2006
Buku Teks
Lucas, Bob, author
American Management Association, 2008
eBooks
edited by J. Graham Beaumont
Grange Books, 1989
Buku Referensi
Brogan, Kelly, author
Thorson, 2016
Buku Teks