McMillon, Bill, author
John Wiley & Sons, 1991
Buku Referensi
Lawson, Joseph W.R., II, author
American Management Association, 1998
eBooks
Brewer, Richard, author
Saunders College Publishing, 1982
Buku Teks
Benton, Allen H., author
Burgess Publishing Company, 1972
Buku Teks
Escoe, A. Keith
Elsevier, 2008
Buku Teks