1. School of Agricultural Economics and Rural Development; Renmin University of China; Beijing China
2. Department of Psychological Medicine; National University of Singapore; Singapore Singapore
3. Department of Statistics and Applied Probability; National University of Singapore; Singapore
4. Center for the Study of Aging and Human Development; Duke University; Durham North Carolina
5. Geriatrics Division; School of Medicine; Duke University; Durham North Carolina
6. Center for Healthy Aging and Development Studies; National School of Development; Peking University; Beijing China