Bardbury, Mary
Routledge, 1999
Buku Teks
Ratner, Carl, author
Lawrence Erlbaum Associates, 2006
Buku Teks
Lindesmith, Alfred R., author
Holt, Rinehart and Winston, 1956
Buku Teks
American Psychological Assosiation, 2004
Majalah, Jurnal, Buletin
Ashford, Jose B., author
Wadsworth, 2001
Buku Teks