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: the Industrial Labor Relations Review (ILRReview), October 2015; vol. 68, 5: pp. 1043-1077