Levine, Karen
Vermont Storey Books, 1996
Buku Teks
Sincero, Jen, author
Running Press, 2017
Buku Teks
Maxwell, John C., author
MIC , 2016
Buku Teks
Koch, Richard, author
Bhuana Ilmu Populer, 2004
Buku Teks
Smith, Jim, author
American Society for Training & Development, 2008
eBooks