Uma Sekaran
Tata McGraw-Hill, 1995
Buku Teks
Ticehurst, George William, author
Longman, 2000
Buku Teks
Furlong, Nancy E., author
Harcourt College Publishers, 2000
Buku Teks
Bordens, Kenneth S., author
McGraw-Hill, 2002
Buku Teks
Bordens, Kenneth S., author
McGraw-HIll, 2005
Buku Teks