Haueisen, William D.
Prentice-Hall, 1982
Buku Teks
Gwartney, James D.
FL. The Dryden Press, 1995
Buku Teks
James, Clifford L.
Prentice-Hall, 1951
Buku Teks
Gwartney, James D.
Harcourt Brace Jovanovich, Publisher, 1987
Buku Teks
American Public Health Association, 1978
Buku Teks