To cite parfm in publications use:

Marco Munda, Federico Rotolo, Catherine Legrand (2012). parfm: Parametric Frailty Models in R. Journal of Statistical Software, 51(11), 1-20. URL http://www.jstatsoft.org/v51/i11/.

Corresponding BibTeX entry:

  @Article{,
    title = {{parfm}: Parametric Frailty Models in {R}},
    author = {Marco Munda and Federico Rotolo and Catherine Legrand},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {51},
    number = {11},
    pages = {1--20},
    url = {http://www.jstatsoft.org/v51/i11/},
  }