McLachlan, G., A. Ng, P. Adams, D. C. McGiffin, and A. Gailbraith. “An Algorithm for Fitting Mixtures of Gompertz Distributions to Censored Survival Data”. Journal of Statistical Software, vol. 2, no. 7, Nov. 1997, pp. 1-23, doi:10.18637/jss.v002.i07.