As part of the baseline data collection a quality control survey was conducted to ascertain the reproducibility of initial results. This survey involved over 15,000 participants (3.1% of the total participants) and typically took place within 4-6 weeks of the baseline survey. It focused on several key questionnaire variables (smoking, alcohol drinking, tea consumption, number of hours slept, and, for women, aspects of reproductive history) and the measurement of blood pressure.
After the initial baseline survey, three resurveys were conducted in 2008, 2013-14, and 2020-21 involving a random subset of about 5% of the original participants. As well as repeating the data collection as at the baseline), many enhancements were made, including new physical measurements (e.g. 12-lead ECG, carotid IMT, ankle blood pressure, heel bone mineral density, liver fibrosis, and retinal imaging), improved measures of physical activity and sleep using wearable devices, and collection of new biological samples (e.g. urine, saliva and faecal). The overall response rate was more than 80% in each of the three resurveys.
Daily meteorological measurements between 2004 and 2008 were also obtained from the local offices of the China Meteorological Administration in each regional study area. They included information on air pressure; temperature; humidity; precipitation and wind speed.