5 IZA Discussion Papers
IZA Discussion Paper No. 4674
IZA Discussion Paper No. 2712
revised version published in: Applied Economics Letters, 2009, 16 (11), 1165 - 1169
IZA Discussion Paper No. 2520
IZA Discussion Paper No. 2131
published in: American Economic Review, 2010, 100 (5), 1999-2030
IZA Discussion Paper No. 316
published in: Economics Letters, 2003, 80 (1), 5-21