∗The authors would like to thank the Editor and a referee for some very thoughtful and constructive comments on an earlier draft of the paper. This research has been supported by Australian Research Council Discovery Grant No. DP0208333 and a Ph.D. Scholarship from the School of Business Systems, Monash University. All numerical results in the paper have been produced using the MATLAB software. †JEL Codes: C11, C15, C52, E43.