Henry, Nicholas
Prentice-Hall, 1975
Buku Teks
Simon, Herbert A.
Alfred A. Knopf, 1973
Buku Teks
Bartholomew, Paul C.
Littlefield, Adams, 1959
Buku Teks
edited by Robert T. Golembiewski, Frank Gibson, Geoffrey Y. Cornog
Rand McNally College, 1972
Buku Teks
Pfiffner, John M.
Ronald Press, 1960
Buku Teks