Denham, Paul
Stanley Thornes, 1987
Buku Teks
edited by A.T. Dalfovo
The Council for Research in Values and Philosophy , 2002
Buku Teks
Sniderman, Paul M
University of California Press, 1981
Buku Teks
Forsythe, David P., 1941-, author
University of Nebraska Press, 1983
Buku Teks
Schenkman publishing Company, Inc., 1971
Buku Teks