Orsolya Lelkes is an Economic Policy Analyst and Research Fellow at the European Centre for Social Welfare Policy and Research. She is also a research affiliate at the Centre for Analysis of Social Exclusion (CASE) at the London School of Economics. From 2002 to 2005 she was the head of the Economics Research Unit at the Ministry of Finance in Hungary and the national representative at the Council of Europe Economic Policy Committee in Brussels. Holly Sutherland is a Research Professor at ISER, University of Essex. She has 25 years experience in designing, building and using tax-benefit models. She has published widely in economics and social policy journals and she is the co- author (with G. Redmond and M. Wilson) of The Arithmetic of Tax and Social Security Reform and the co- editor (with L. Mitton and M. Weeks) of Microsimulation Modelling for Policy Analysis: Challenges and Innovations.