Institution: | 1 Department of Statistics and Applied Probability, National University of Singapore, Singapore staxyc{at}stat.nus.edu.sg, 2 Institute of Mathematics & Statistics, University of Kent, Canterbury, Kent CT2 7NF, U.K. w.zhang{at}kent.ac.uk, 3 Department of Statistics & Actuarial Science, The University of Hong Kong, Pokfulam Road, Hong Kong htong{at}hku.hk |