Abiodun, A. A., B. A. Oyejola, and K. A. Adeleke. “An Empirical Comparison Between Partial Likelihood and Penalized Partial Likelihood Estimators for Semi-Parametric Non-Proportional Hazards Models With Frailty”. Malaysian Journal of Applied Sciences, Vol. 4, no. 1, June 2019, pp. 1-14, https://journal.unisza.edu.my/myjas/index.php/myjas/article/view/124.