3 IZA Discussion Papers
IZA Discussion Paper No. 799
published in: Oxford Economic Papers, 2005, 57 (1), 169-189
IZA Discussion Paper No. 549
revised version published in: American Economic Review, 2006, 96 (3), 811-831
IZA Discussion Paper No. 384
published in: Research in Labor Economics 22, 2003, 159-202