Biech, Elaine, author
American Society for Training & Development, 2005
eBooks
Laurel Saville, Steve Gordhan, Jodhua Berger, Sarch Dougher, editor
Page one publishing pte ltd, 2011
Buku Referensi
Thompson, Willard M.
McGraw-Hill , 1968
Buku Teks
Donatelle, Rebecca J., author
Allyn and Bacon , 1997
Buku Teks
Macionis, John J., author
Prentice-Hall, 2000
Buku Teks