... refractions in Western China. In order to obtain the refractive status in school-age children in Western China, we selected Yongchuan District, Chongqing, a representative dis-trict in Western China, ... China. China statistical year-book 2003 [in Chinese]. Beijing: China Statistics Press. 2003: 100-102. 19. Chongqing Municipal Bureau of Statistics. Chongqing statistic-al yearbook 2004 [in ... being ranked middle in Western China and most residents in this district being Han Chinese. In this study, clusters were defined by geo-graphical residential areas, called residence adminis-trative...