Fraser, T.G.
Macmillan Press, 1995
Buku Teks SO
Siagian, Siar Anggretta
Program Pascasarjana Universitas Indonesia, 2007
UI - Tesis Membership
Blackwell, 2005
eBooks
Birmingham, David
Cambridge University Press, 1993
Buku Teks SO
Heidhues, Mary Somers
Thames dan Hudson , 2000
Buku Teks SO