5 IZA Discussion Papers
IZA Discussion Paper No. 9981
IZA Discussion Paper No. 8214
IZA Discussion Paper No. 5985
IZA Discussion Paper No. 3784
revised version published in: Journal of Labor Economics, 2011, 29 (3), 513-547
IZA Discussion Paper No. 1143
published in: Economic Journal, 2009, 119 (539), 1208 - 1224