1. Institute of Health Management and Policy, School of Public Policy and Administration, Xi'an Jiaotong University, Xi'an, China
2. Department of Education and Training, Liverpool School of Tropical Medicine, Liverpool, UK
3. Department of Clinical Sciences, Liverpool School of Tropical Medicine, Liverpool, UK
4. Department of Epidemiology and Health Statistics, School of Public Health, Center of Medical Science, Xi’an Jiaotong University, Xi’an, PR China