4 IZA Discussion Papers
IZA Discussion Paper No. 9439
published in: Ecological Economics, 2015, 120, 234-240.
IZA Discussion Paper No. 7988
IZA Discussion Paper No. 3407
published in: American Economic Review, 2008, 98 (2), 49-53
IZA Discussion Paper No. 2976
published in: Journal of Human Resources, 2009, 44 (1), 251 - 276