The authors are grateful to the editors and referees for their comments and suggestions which have much improved the presentation. This research was supported by the NNSF of China (10471057) and (50808025).
Zehui Li is a Professor of Probability and Statistics at the School of Mathematics and Statistics and the Director of the Institute of Mathematical Statistics and Reliability Theory of Lanzhou University. She has completed three projects of the National Natural Science Foundation of China. Professor Li’s research interests include counting processes and their applications, applied statistics, reliability, survival analysis, risk theory and asymptotic theory. Her papers have appeared in well-known journals, such as European Journal of Operational Research, Journal of Statistical Planning and Inference, IEEE Transactions on Reliability, Statistics and Probability Letters, International Journal of Reliability and Quality and Safety Engineering.
