ZEILEIS, A. Object-oriented Computation of Sandwich Estimators. Journal of Statistical Software, [S. l.], v. 16, n. 9, p. 1–16, 2006. DOI: 10.18637/jss.v016.i09. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v016i09. Acesso em: 21 may. 2022.