1. Department of Sociology, Tsinghua University, Beijing, China
2. Department of Community Health Sciences, University of California, Los Angeles, California, USA
3. Division of Sleep Medicine, Beijing University People’s Hospital, Beijing, China
4. Department of Sociology and Aging Studies Institute, Maxwell School of Citizenship and Public Affairs, Syracuse University, Syracuse, New York, USA
5. Vanke School of Public Health, Tsinghua University, Beijing, China
6. Department of Social and Behavioural Sciences, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA