Hughes, Emmet John
Atheneum, 1963
Buku Teks SO
MacNeil, Robert
Viking Penguin, 1989
Buku Teks SO
Hari, Daoud
Random House, 2008
Buku Teks SO
Garber, Peter R.
American Society for Training & Development, 2012
eBooks
edited by Wolfgang Rodi
Pergamon Press, 1982
Buku Teks