Watts, Alan W., author
John Murray , 1948
Buku Teks
Rasiel, Ethan M
McGraw-Hill, 1999
Buku Teks
Barnett, G. William, author
American Management Association, 2008
eBooks
Epping, Randy Charles, author
Vintage books, 1995
Buku Teks
Maddi, Salvatore R., author
AMACOM, 2005
Buku Teks