Ridge, Warren J., author
Illinois Dow Jones-Irwin , 1973
Buku Teks
May, John
McGraw-Hill , 1983
Buku Teks
Clemens, John, author
American Management Association, 2005
eBooks
Maslen, Andy, author
Marshall Cavendish, 2011
Buku Teks
Baron, Eric, author
Wiley, 2013
Buku Teks