Methods A total of 7482 residents aged 15-69 selected in representative 30 counties through multi-stage random sampling from Zhejiang Province were surveyed by using questionnaire.
方法采用多阶段随机抽样的方法，在浙江省有代表性的30个县区，对7482名年龄在15～69岁的居民进行面对面问卷调查。
Method A multi-stage stratified cluster sampling survey on health condition of 14486 residents was taken in 2007.
方法：采用多阶段分层整群抽样方法，对2007年居民家庭健康状况入户调查，共调查14 486人。
We give the approximation formulas of the variance of the sample ratio estimator for a population mean and its asymptotically non-biased estimator in multi-stage sampling.
讨论多阶段抽样比率估计及其样本量选择的问题，给出了比率估计抽样均方误差的近似公式及其渐近无偏估计的公式。
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