Funding for this research was provided by:
Chinese Government Scholarship (201708310108)
Received: 23 December 2019
Accepted: 16 August 2020
First Online: 24 August 2020
Ethics approval and consent to participate
: Ethics approval was obtained from the ethics review committees of the World Health Organization and the Chinese Center for Disease Control and Prevention. Written consent was obtained from all study participants by the WHO-SAGE research team who collected the data.
: Not applicable.
: Jane Murray Cramm is an associate editor of BMC Geriatrics. The authors declare that they have no other competing interests related to this manuscript.