“…For the BrownProschan model, Lim [15] has studied estimation with the EM-algorithm, Langseth and Lindqvist [13] have estimated parameters on real data set with maximum likelihood, and Lim, Lu and Park [14] have used Bayesian estimation. For virtual age models some studies on maximum likelihood estimators have been published: Shin, Lim and Lie [19], Yun and Choung [21], Kaminskiy and Krivtsov [9], Yanez, Joglar and Modarres [20], Gasmi, Love and Kahle [8], Doyen and Gaudoin [6]. But all these studies only proposed numerical results.…”