Castles, Francis G.
Allen & Unwin, 1985
Buku Teks
Cambridge University Press, 2005
Buku Teks
Mulgan, Richard, author
Oxford University Press, 1989
Buku Teks
Gough, Ian, author
Macmillan, 1992
Buku Teks
James, Colin, author
Allen & Unwin : Port Nicholson Press, 1986
Buku Teks