Cross, Rod
Martin Robertson, 1982
Buku Teks
Artis, M.J.
Department of Economics, University of Manchester, [date of publication not identified]
Buku Teks
George Allen and Unwin, 1963
Buku Teks
Spero, Joan Edelman
Routledge , 1997
Buku Teks
Spero, Joan Edelman
Wadsworth, 2010
Buku Teks