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Study design

The CKB is an open-ended study to enable research across a wide range of areas for both hypothesis testing and generation purposes. Although it follows the design principles of twentieth-century prospective studies, the size, complexity, study methods, breadth and depth of information collected, or to be generated in the CKB goes far beyond the conventions.

population

More than 512,000 adults aged 30 to 79 were recruited from the general population in ten geographically defined and diverse areas of China (five urban and five rural). The study areas were chosen carefully according to local disease patterns, exposure to certain risk factors, population stability, quality of death and disease registries, coverage of health insurance, and local commitment and capacity. 

Map of China showing location of the 10 CKB study sites and number of participants recruited by each site.Map of China showing location of the 10 CKB study sites and number of participants recruited by each site.

 

 

Methods

The CKB involves a detailed baseline survey of study participants with extensive data collection by questionnaire and physical measurements, and collection and long-term storage of blood samples. After the baseline survey, periodic resurveys are conducted every 4-5 years, each involving about 5% of the surviving participants randomly selected from the original cohort, with repeated collection of the same data as at the baseline.

The resurveys allow the relevance of long-term ‘usual’ levels of risk factors to be assessed by allowing appropriate adjustment for regression dilution (AJE, 1999) and other sources of variation. Enhancements can also be considered to address future research questions, including new survey questions, samples and measurements that become possible. The long-term health of study participants is monitored through electronic linkages via the unique personal ID number with established registries and health insurance system, covering cause-specific mortality, major morbidity (stroke, IHD, cancer and diabetes) and episodes of hospitalisation. (IJE, 2005 and IJE, 2011)

fieldwork

In each study area a survey team of about 16 to 18 full-time staff with relevant health-related qualifications and fieldwork experience, was established.

Potentially eligible participants in each of 100-150 administrative units (rural villages or urban residential committees) selected for the study in each area were identified through residential records and invited to complete the surveys. All participants were asked to bring their unique national ID cards to the assessment centre set up in the local community. Each participant registered and provided informed written consent to allow access to their medical records and long-term storage of biological samples for anonymised and non‑specified medical research purposes. They then moved through a series of stations in the study assessment centre. The whole visit typically took between 60 and 90 minutes. All the field work was managed electronically, using a range of bespoke IT systems developed by the CKB.