Dehejia, R. H. and Wahba, S. (1999), "Causal effects in nonexperimental studies: Reevaluating the evaluation of training programs," Journal of the American Statistical Association, 94, 1053-1062.
Firpo, S. (2007), "Efficient semiparametric estimation of quantile treatment effects," Econometrica, 75, 259-276.
LaLonde, R. J. (1986), "Evaluating the econometric evaluations of training programs with experimental data," The American Economic Review, 604-620.