1. School of Medicine, University of North Carolina in Chapel Hill , Chapel Hill, North Carolina , USA
2. School of Education, Virginia Polytechnic Institute and State University , Blacksburg, Virginia , USA
3. Institute for Health, Health Care Policy and Aging Research, Rutgers, The State University of New Jersey , New Brunswick, New Jersey , USA
4. Department of Social Security, School of Labor and Human Resources, Renmin University of China , Beijing , China