East, Roger
Routledge, 2006
Buku Referensi
The American Bibliographical Institute, 1986
Buku Referensi
Schuman, Frederick L.
McGraw-Hill, 1958
Buku Teks
Murphy, Robert F.
Columbia University Press, 1972
Buku Teks
World Bank
World Bank, 1981
Buku Teks