ZEILEIS, A.; CROISSANT, Y. Extended Model Formulas in R: Multiple Parts and Multiple Responses. Journal of Statistical Software, [S. l.], v. 34, n. 1, p. 1–13, 2010. DOI: 10.18637/jss.v034.i01. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v034i01. Acesso em: 21 may. 2022.