Downs, Anthony, author
Markham Publishing, 1970
Buku Teks
Palen, J. John, author
McGraw-Hill, 1992
Buku Teks
Palen, J. John, author
McGraw-Hill, 1981
Buku Teks
Liston, Robert A., author
Dell Publishing, 1968
Buku Teks
edited by David Popenoe
Rutgers University Press, 1969
Buku Teks