Egbert, Richard T.
Prentice-Hall, 1991
Buku Referensi
Hindle, Tim, author
Harvard Business, 1993
Buku Referensi
Weisinger, Hendrie, author
American Management Association, 2000
eBooks
Hoevemeyer, Victoria A., author
American Management Association, 2006
eBooks
Jones, E.B., author
Pitman, 1972
Buku Teks