Funding for this research was provided by:
China Medical Board (17-274)
National Natural Science Foundation of China (81703320, 82073665)
Received: 21 October 2020
Accepted: 23 April 2021
First Online: 3 May 2021
: All subjects provided informed consent for inclusion prior to participating in the fifth National Health Services Survey in Guangdong province. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Medical Ethics Committee of the School of Public Health, Sun Yat-sen University (No. 130 in 2020).
: Not applicable.
: The authors declare that they have no competing interests.