Allignol, Arthur, Martin Schumacher, and Jan Beyersmann. “Empirical Transition Matrix of Multi-State Models: The Etm Package”. Journal of Statistical Software 38, no. 4 (January 4, 2011): 1–15. Accessed May 28, 2022. https://www.jstatsoft.org/index.php/jss/article/view/v038i04.