To cite p3state.msm in publications use:

Luis Meira-Machado, Javier Roca Pardinas (2011). p3state.msm: Analyzing Survival Data from an Illness-Death Model. Journal of Statistical Software, 38(3), 1-18. URL http://www.jstatsoft.org/v38/i03/.

Corresponding BibTeX entry:

  @Article{,
    title = {{p3state.msm}: Analyzing Survival Data from an
      Illness-Death Model},
    author = {Lu\'{\i}s Meira-Machado and Javier Roca Pardi\~{n}as},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {38},
    number = {3},
    pages = {1--18},
    url = {http://www.jstatsoft.org/v38/i03/},
  }