Zimmerman, Neal, author
John Wiley & Sons, 1996
Buku Teks
Ennico, Cliff, author
American Management Association, 2007
eBooks
Moss, Stephen R., author
Prentice-Hall, 2001
Buku Teks
DePamphilis, Donald, author
Elsevier , 2011
Buku Teks
Stebben, Gregg, author
Pocket Books, 1999
Buku Referensi