Fox, Michael W.
University Park Press, 1983
Buku Teks
New York : macmillan Library reference USA, 1997,
Buku Referensi
Begon, Michael
Sinauer Associates, 1986
Buku Teks
Drucker, Peter Ferdinand, 1909-2005
Truman Talley Books/Plume, 1992
Buku Teks
Stephens, Mitchell
Coloumbia University Press , 2014
Buku Teks