ESOMAR, 1972
Buku Teks
Gandhi, J.C.
McGraw-Hill Publishing Company, 1995
Buku Teks
Bingham, Frank G., author
NTC/Contemporary Publishing Group, 2001
Buku Teks
Robinson, Patrick J.
Allyn & Bacon, Inc., 1967
Buku Teks
Perreault, William D., author
Irwin McGraw-Hill, 1999
Buku Teks