aDepartment of Economics, Waikato Management School, The University of Waikato, Private Bag 3105, Hamilton, New Zealand
bDepartment of Economics, Private Bag 4800, University of Canterbury, Christchurch, Canterbury, New Zealand
Received 9 January 2004;
revised 9 April 2004;
accepted 24 September 2004.
Available online 8 December 2004.