Morrell, James
Penguin Books, 1972
Buku Teks
Makridakis, Spyros G., author
The Free Press, 1990
Buku Teks
edited by Arch G. Woodside
Emerald, 2016
eBooks
Michel-Kerjan, Erwann, author
Public Affairs, 2010
Buku Teks
Cooke, Steve
Prentice-Hall, 1991
Buku Teks