Nietzel, Michael T., author
Prentice-Hall, 1998
Buku Teks
Sarafino, Edward P., author
John Wiley & Sons, 1994
Buku Teks
American Psychological Assosiation, 2007
Majalah, Jurnal, Buletin
Richards, Thomas William
McGraw-Hill, 1946
Buku Teks
Kendall, Philip C., author
John Wiley & Sons, 1982
Buku Teks