Vermunt, Jeroen K. “Multilevel Latent Variable Modeling: An Application in Education Testing”. Austrian Journal of Statistics 37, no. 3&4 (April 3, 2016): 285–299. Accessed May 10, 2021. https://ajs.or.at/index.php/ajs/article/view/vol37%2C%20no3%264%20-%206.