edited by Robert T. Golembiewski, Frank Gibson, Geoffrey Y. Cornog
Rand McNally College, 1972
Buku Teks
Simon, Herbert A.
Alfred A. Knopf, 1973
Buku Teks
Denhardt, Robert B.
Harcourt College, 1999
Buku Teks
Bartholomew, Paul C.
Littlefield, Adams, 1959
Buku Teks SO
Henry, Nicholas
Prentice-Hall, 1975
Buku Teks SO