RIZOPOULOS, D. ltm: An R Package for Latent Variable Modeling and Item Response Analysis. Journal of Statistical Software, [S. l.], v. 17, n. 5, p. 1–25, 2006. DOI: 10.18637/jss.v017.i05. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v017i05. Acesso em: 27 nov. 2021.