@article{Heckman1997,
author = {Heckman, J.J. and Ichimura, H. and Todd, P.E. },
title= {Matching as an econometric evaluation estimator: Evidence from evaluating a job training programme},
year = {1997},
doi = {10.2307/2971733},
journal = {Review of Economic Studies },
volume = {64},
number = {4},
pages = {605--654},
}