Gardner, Fred V.
McGraw-Hill, 1940
Buku Teks
MacDonald, John Haskell, 1896
Prentice-Hall, 1939
Buku Teks
Edey, Harold C.
Hutchinson's University Library , 1972
Buku Teks
Waagen, Alice K., author
American Society for Training & Development Press, 2000
eBooks
Pyhrr, Peter A., author
John Wiley & Sons, 1973
Buku Teks