Shacford, R.H.
Public Affairs Press, 1952
Buku Teks
Kang, Woobang
Art Media Resources, 2005
Buku Teks
Larry Israelite, editor
American Society for Training & Development, 2006
eBooks
Wrenn, Chase B., 1974-
Polity, 2015
Buku Teks
Grey, Johnny
A Cassell Book, 1994
Buku Referensi