American Psychological Association, {s.a}
Majalah, Jurnal, Buletin
edited by Cynthia Jeffrey
Emerald, 2016
eBooks
Hansen, Don R., author
South-Western College Publishing, 2000
Buku Teks
Norgaard, Corine T., author
Prentice-Hall, 1985
Buku Teks
Khan, M.Y., author
McGraw-Hill, 1985
Buku Teks