4 IZA Discussion Papers
IZA Discussion Paper No. 9295
IZA Discussion Paper No. 7455
IZA Discussion Paper No. 6535
revised version published in: Labour Economics, 2013, 21 (1), 25-41
IZA Discussion Paper No. 5677
published in: ILR Review, 2015, 68 (5), 1043-1077