Keegan, Warren J., author
Prentice Hall International, 1989
Buku Teks
Keegan, Warren J., author
Prentice Hall International, 1995
Buku Teks
Boyd, Harper W., Jr., author
Irwin, 1995
Buku Teks
Sheth, Jagdish N., author
Ohio South-Western Pub, 1989
Buku Teks
Lamont, Douglas, author
Blackwell Publishers, 1996
Buku Referensi