STBS , 1991
Buku Teks
Boner, Roger Alan, author
World Bank, 1993
Buku Teks
Elkin, A. P., author
Oxford University Press, 1953
Buku Teks
Philippines : De La Salle Univesrsity-Manila, 2005,
Majalah, Jurnal, Buletin
Erwin Ramedhan, author
2005
Artikel Jurnal