edited by Ray Woolfe, Windy Dryden, Sheelagh Strawbridge
Sage Publications, 2003
Buku Referensi
Hahn,Milton E.
McGraw-Hill Book Co., 1955
Buku Teks
American Psychological Association, 2018
Majalah, Jurnal, Buletin
Sage, 2001
Buku Teks
Tschudin, Verena, author
Bailliere Tindall , 1995
Buku Teks