Andrews, Richard B., author
The Free Press, 1971
Buku Teks
Due, John F.
Richard D. Irwin, Inc., 1969
Buku Teks
Garfield, Paul J.
Prentice-Hall, 1964
Buku Teks
Duff, Lois, author
Longman, 1997
Buku Teks
Gwartney, James D.
Harcourt Brace Jovanovich, Publisher, 1987
Buku Teks