BADA, O.; LIEBL, D. phtt: Panel Data Analysis with Heterogeneous Time Trends in R. Journal of Statistical Software, [S. l.], v. 59, n. 6, p. 1–33, 2014. DOI: 10.18637/jss.v059.i06. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v059i06. Acesso em: 15 aug. 2022.