3 IZA Discussion Papers
IZA Discussion Paper No. 9556
revised version published in: Journal of Applied Econometrics, 2019, 34 (3), 403 - 424
IZA Discussion Paper No. 6544
published in: Empirical Economics, 2015, 49, 1123-1141
IZA Discussion Paper No. 3039
completely revised published in: Oxford Bulletin of Economics and Statistics, 2009, 71 (5), 659-681