Kennedy, Paul M
Vintage Books, 1993
Buku Teks
Newell, Michael W., author
American Management Association, 2005
eBooks
Ag. Bambang Setiyadi, author
Graha Ilmu, 2018
Buku Teks
Artikel Jurnal
Record, Matthew, author
Glorier International, 1999
Buku Referensi