Methods: The review epidemiological investigation research in 9 countries 52 villgaes of Panshi, Liaoyuan, Baishan, Jilin province had been done by random chester sampling.

 
  • 方法:用分层随机整群抽样方法对吉林省磐石、辽源、白山3市9个乡、52个村进行回顾性流行病学调查研究。
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