Carnes, W. Stansbury
HarperBusiness, 1992
Buku Referensi
Perthel, Dirk
Amsterdam University, 1981
Buku Teks
Doody, Francis S.
New York, N.Y. Random c.1965,
Buku Teks
Carrington, Richard
Penguin Books, 1958
Buku Teks
Stutely, Richard
The Economist Books, 1992
Buku Teks