2 IZA Discussion Papers
IZA Discussion Paper No. 1512
published in: Millimet, D., Smith, J. and Vytlacil, E. (eds.), Advances in Econometrics, Volume 21: Estimating and Evaluating Treatment Effects in Econometrics, 2008, 383-430,
IZA Discussion Paper No. 750
published in: Research in Economics, 2004, 58(4), 257-302