8Rosenbaum, P. , Rubin, D. Constructing a Control Group Using Multivariate Matched Sampling Method that Incorporates the Propensity Score. American Statistician, 1985 ( 39 ) : 33 - 38.
9Heckman,J. J. , Iehimura, H. ,Todd,P. E. Matching as an Econometric Evaluation Estimator: Evidence from Evaluating a Job Training Program. Review of Economic Studies, 1997 (4) : 605 - 654.
