Balan, Theodor Adrian, and Hein Putter. “FrailtyEM: An R Package for Estimating Semiparametric Shared Frailty Models”. Journal of Statistical Software 90, no. 7 (July 31, 2019): 1–29. Accessed May 2, 2024. https://www.jstatsoft.org/index.php/jss/article/view/v090i07.