2010
Majalah, Jurnal, Buletin
Philippines : De La Salle University Manila, 2008,
Majalah, Jurnal, Buletin
Boston : Harvard Business School Press, 2004,
Buku Teks
Shao, Stephen P.
Virginia s.n,
Buku Teks
Harahap, P.R.
Jakarta Praninta Aksara [date of publication not identified],
Buku Teks