二次抽样是按照随机原则从同一统计总体中分两次抽取两个样本，并根据这两个样本来推断总体情况的抽样方式。
如果二次抽样检验仍记录为不合格，则该批次所有物项全部拒收。
Further recorded non compliance's will result in the entire batch being rejected.
方法按照第二次全国口腔健康流行病学调查标准，对两镇3 ~ 74岁人群进行龋病流行病学抽样调查。
Methods According to the standard of the second national oral health epidemiological investigation, the incidence of caries in 3 ~ 74-year-old residents of the two town were examined.
利用2006年上海市第二次全国残疾人抽样调查资料，分析上海市残疾老人的基本特征和致残状况。
By using Shanghai's data from the Second National Sample Survey on disability in 2006, the paper analyses characteristics and disability of Shanghai's old disabled people.
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