American Psychological Association, 2005
Buku Teks
American Psychological Association, 2004
Buku Teks
edited by Robert D. Morgan, Tara L. Kuther, Corey J. Habben
Psychology Press, 2005
Buku Teks
Cambridge Hobsons 1987
Buku Referensi
UK : The Association of Commonwealth Universities, 1988,
Buku Referensi