Boguslaw, Robert
Prentice-Hall, 1965
Buku Teks
Maher, Robert F.
The University of Wisconsin Press, 1961
Buku Teks
Lauer, Robert H., author
Allyn and Bacon, 1982
Buku Teks
Schratz, Michael, author
Routledge, 1995
Buku Teks
Mayer, Robert R., author
Prentince-Hall, 1980
Buku Teks