@article{Heckman1985,
author = {Heckman, J. J. and Robb, R.},
title= {Alternative methods for evaluating the impact of interventions: An overview},
year = {1985},
doi = {10.1016/0304-4076(85)90139-3},
journal = {Journal of Econometrics},
volume = {30},
number = {1},
pages = {239--267},
}