Philip, Tom, author
McGraw-Hill, 1983
Buku Teks
by David L. Devries ... [et.al.]
John Wiley, 1981
Buku Teks
Artikel Jurnal
Ari Saptari, author
Fakultas Psikologi Universitas Indonesia, 2007
UI - Skripsi (Membership)
Kirkpatrick, Donald L., author
AMACOM, 2006
Buku Teks