4 IZA Discussion Papers
IZA Discussion Paper No. 2688
IZA Discussion Paper No. 2465
published in: Labour, 22 (4), 2008, 569 - 591
IZA Discussion Paper No. 1651
published in: Industrial and Labor Relations Review, 2006, 60 (1), 105-119
IZA Discussion Paper No. 881
published in: Economica, 2006, 73 (290), 287-298