@article{Heckman1998,
author = {Heckman, J. and Ichimura, H. and Todd, P. E.},
title= {Matching as an econometric evaluation estimator},
year = {1998},
doi = {10.1111/1467-937X.00044},
journal = {Review of Economic Studies},
volume = {65},
pages = {261--294},
}