Affiliation: | aThe Camford Group, 13 High Street, Cottenham, Cambridge CB4 4SA, UK Tel: +44 1954 206236; fax: +44 1954 206237;bDepartment of Economics, Brunel University, Uxbridge, Middlesex UB8 2PH, UK Tel: +44 189E 203320; fax: +44 1895 274697;cAll Souls College, Oxford OX1 4AL, UK Tel: +4 1865 279313; fax: +44 1865 279299 |