Sage, 2008
eBooks
Gomm, Roger
Palgrave-Macmillan, 2004
Buku Teks SO
SEAMIC, 1988
Buku Teks SO
California : The Institute of International Studies, University of California, 1993
Majalah, Jurnal, Buletin
Kish, Leslie
John Wiley & Sons, 1965
Buku Teks SO