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【多选题】
下面关于抽样方法的说法,哪些是正确的?A.
偶遇抽样时，因为调查对象时随机选取的，事先不认识，所以这是一种随机抽样方法。
B.
定额抽样和分层抽样都是对总体进行分层分类，所以本质上都是概率抽样方法。
C.
在同等条件下，减少多段抽样误差的方法是，相对增加开头阶段的样本数，适当减少最后阶段的样本数。
D.
判断抽样的优点是可以发挥研究人员的主观能动性，特别是当研究人员对研究总体的情况熟悉，研究经验丰富时，是一种比较便捷的抽样方法。
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