Smolensky, Jack
W.B. Saunders Company, 1972
Buku Teks SO
Gray, Stephen E.
MacMillan Press , 1978
Buku Teks
Herman, Harold
International City Managers Association, 1968
Buku Teks
edited by Robert D. Newcomb, Jerry L. Jolley
Charles C. Thomas, 1980
Buku Teks
Livingstone, 1983
Buku Teks