@article{Rosenbaum1983,
author = {Rosenbaum, P. and Rubin, D.},
title= {The central role of the propensity score in observational studies for causal effects},
year = {1983},
doi = {10.1093/biomet/70.1.41},
journal = {Biometrika},
volume = {70},
number = {1},
pages = {41--55},
}