1. Faculty of Political Economy, University of Economics and Business, Vietnam National University, Room 100, Building E4, 144 Xuan Thuy Road, Cau Giay District, Hanoi, Vietnam, qtt1@waikato.ac.nz, tuyentq@vnu.edu.vn
2. Department of Economics, University of Waikato, Hamilton Campus, Gate 1, Knighton Road, Private Bag 3105, Hamilton 3240, New Zealand, slim1@waikato.ac.nz
3. Department of Economics, University of Waikato, Hamilton Campus, Gate 1, Knighton Road, Private Bag 3105, Hamilton 3240, New Zealand, mcam@waikato.ac.nz
4. Department of Economics, University of Waikato, Hamilton Campus, Gate 1, Knighton Road, Private Bag 3105, Hamilton 3240, New Zealand, vhv1@waikato.ac.nz