Laski, Harold J.
George Allen and Unwin, 1936
Buku Teks
Juhl, P.D.
Princeton University Press, 1980
Buku Teks
Dickinson, Robert E.
Routledge & Kegan Paul Limited, 1951
Buku Teks
Erwin Ramedhan
2005
Artikel Jurnal
Portnoy, Ethel
Meulenhoff, 1998
Buku Teks