Morgan, Theodore, author
Prentice-Hall, 1950
Buku Teks
Cairncross, Alec, author
Butterworth, 1960
Buku Teks
Johnson, Alvin S., author
Hearh & Co., 1911
Buku Teks
Novack, Clare, author
[American Society for Training & Development Press, American Society for Training & Development Press], 2001
eBooks
Hicks, John R., author
The Clarendon Press, 1952
Buku Teks