CCCO was initiated in 2016 and is being conducted in nine centres across six cities. The cities are in the east, west, middle, south, north, and north-east of China. These sites were selected based on the abilities of the local investigators to administer the survey consistently, the existence of suitably qualified doctors to diagnose osteoporosis, and relatively fixed communities in those regions. Female residents aged between 45 and 80 and male residents aged between 50 and 80 years old were identified through permanent resident lists. Residents who responded and completed the first survey were re-surveyed annually for the first 5 years and then every 5 years later.