Downes, John
Barron's Educational Series, 1998
Buku Referensi
Downes, John, author
barron's, 2006
Buku Teks
Hildreth, Sandra S., author
Dearborn Financial Publishing, 1988
Buku Referensi
Jordan, John E.
Harper & Row, Publishers, 1965
Buku Teks
Oxford University Press, 1993
Buku Referensi