Sample Size, Sampling, and Recruitment Procedure

On the basis of the Nanshan population size (18 years or older) of 1,356,307 at the end of 2016 (17), we assumed that the expected prevalence of all chronic diseases was 30%, with consideration of 5% type I error. Thus, we needed 2,800 participants to achieve 80% power for our study. We used a stratified random sampling approach to recruit participants. First, we determined the number of needed participants in each age group (aged 18–24, 25–34, 35–44, 45–54, 55–64, and 65 years or older) by referring to the distribution of age and gender in Nanshan population (17). HUST Union Shenzhen Hospital had records of the Nanshan residents who had registered at the community health service centers. These residents visited the service centers for body check or health consultation regularly. In March 2018, the principal investigator from PolyU conducted a workshop for all head nurses working in the 24 selected community centers to train them about the recruitment process and data collection approaches. Then, the head nurses trained their centers' nurses for subject recruitment and data collection. Since May 2018, the trained nurses started to randomly invite potential participants who visited the service centers to join the study. Subsequently, they screened these potential participants following the inclusion and exclusion criteria. We considered those who met the eligibility criteria, and the eligible participants in our study provided written informed consents. Afterward, we conducted the data collection process. The recruitment lasted for 6 months.