 Randomization: A two-stage and clustered random sampling method is used to select a representative sample of children across Kashgar area. The sampling process is initially stratified the 12 regions of Kashgar area Kashi, Taxian, Shule, Zhepu, Yuepu, Bachu, Maigaiti, Yuecheng, Jiashi, Shufu, Shache, and Yingjisha in descending order by Gross Domestic Product GDP 2014. The first tier is selected two regions by simple random sampling in the first six regions and the last six regions separately. Then the selected regions are stratified by the degree of urbanization urban area vs rural area, and one community in urban area and one village in rural area is selected by randomization. At last four communities in urban area and four villages in rural area are selected across Kashgar area. Children those aged 0 to14 years in these selected communities and villages were all our target population. 