@article{calonico2019covariates,
  author = {Calonico, Sebastian and Cattaneo, Matias D. and Farrell, Max H. and Titiunik, Rocio},
  title = {Regression Discontinuity Designs Using Covariates},
  journal = {Review of Economics and Statistics},
  year = {2019},
  volume = {101},
  number = {3},
  pages = {442--451},
  doi = {10.1162/rest_a_00760}
}