TOOMET, O.; HENNINGSEN, A. Sample Selection Models in R: Package sampleSelection. Journal of Statistical Software, [S. l.], v. 27, n. 7, p. 1–23, 2008. DOI: 10.18637/jss.v027.i07. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v027i07. Acesso em: 21 may. 2022.