Monaco, John V., Malka Gorfine, and Li Hsu. “General Semiparametric Shared Frailty Model: Estimation and Simulation With FrailtySurv”. Journal of Statistical Software 86, no. 4 (September 3, 2018): 1–42. Accessed April 18, 2024. https://www.jstatsoft.org/index.php/jss/article/view/v086i04.