Pasricha, Neil, author
G.P. Putnam's Sons, an imprint of Penguin Random House LLC, 2016
Buku Teks
Smith, Jim, author
American Society for Training & Development, 2008
eBooks
Hamilton, Mark, author
Neo-tech books, 2000
Buku Teks
Sincero, Jen, author
Running Press, 2017
Buku Teks
Chicago Urantia Foundation 1995,
Buku Teks