Rondeau, Virginie, Yassin Marzroui, and Juan R. Gonzalez. 2012. “Frailtypack: An R Package for the Analysis of Correlated Survival Data With Frailty Models Using Penalized Likelihood Estimation or Parametrical Estimation”. Journal of Statistical Software 47 (4):1-28. https://doi.org/10.18637/jss.v047.i04.