Scott, James C.
Yale University Press, 1976
Buku Teks SO
Fifield, Russell H.
Praeger , 1963
Buku Teks SO
editor, Syed Farid Alatas
National Library, 2010
Buku Referensi
Grubel, Herbert G.
Lexington Books, 1973
Buku Teks SO
N.Y. Praeger , 1971
Buku Teks SO