@article{Ho2007,
author = {Ho, D. and Imai, K. and King, G. and Stuart, E.},
title= {Matching as nonparametric preprocessing for reducing model dependence in parametric causal inference},
year = {2007},
doi = {10.1093/pan/mpl013},
URL = {http://gking.harvard.edu/files/abs/matchp-abs.shtml},
journal = {Political Analysis},
volume = {15},
number = {3},
pages = {199--236},
}