O`Donnell, Gerard, author
Macmillan, 1994
Buku Teks
Schrag, Clarence C., author
Harper & Row, 1963
Buku Teks
Zanden, James W. Vander, author
John Wiley & Sons, 1979
Buku Teks
Ogburn, William F., author
Houghton Mifflin, 1946
Buku Teks
Brikerhaff, David B
West Publishing, 1988
Buku Teks