Sohlman, Asa
Stockholm University of Stockholm 1981,
Buku Teks
William Damon, editor-in-chief
John Wiley & Sons, 1998
Buku Referensi
editors, Hans G. Schuetze, German Alvarez Mendiola
Sense, 2012
eBooks
Rees, Teresa, author
Routledge, 1998
Buku Teks
Artikel Jurnal