3 IZA Discussion Papers
IZA Discussion Paper No. 2905
see IZA DP 7199 for a substantially revised and extended version
IZA Discussion Paper No. 1450
revised version published in: Economic Journal, 2008, 118(531), 1354-1384
IZA Discussion Paper No. 585
revised version published in: American Economic Review, 2005, 95 (5), 1653-1672