4 IZA Discussion Papers
IZA Discussion Paper No. 7784
IZA Discussion Paper No. 5644
earlier version published in: Journal of Institutional and Theoretical Economics, 2004, 160 (2), 232-42
IZA Discussion Paper No. 5058
published in: O. Ashenfelter and D. Card (eds.), Handbook of Labor Economics, Vol. 4A, Chapter 8, Amsterdam: Elsevier, 2011
IZA Discussion Paper No. 4100
revised version published in: Journal of European Social Policy, 2011, 21(1), 73-87