1. National School of Development, Peking University, No. 5 Yiheyuan Road, Beijing 100871, China
2. Business School, Imperial College London, South Kensington Campus, Exhibition Rd, London SW7 2AZ, UK
3. Department of Global Health and Population, Harvard T.H. Chan School of Public Health, 677 Huntington Avenue, Boston, Massachusetts 02115, USA
4. Department of Health Policy and Management, School of Public Health, Peking University Health Science Center, No. 38 Xueyuan Road, Beijing 100191, China