该文讨论了为PPS抽样的二相抽样时，其样本单位数的最优设计问题。并结合实例进行了分析。

In this paper, we given an approach for optimum design of sample sire in two-phase sampling for PPS, and discussed an example.

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影响抽样误差大小有很多因素，如标志变异程度，样本单位数量的多少，抽样方式方法的选择等。

There are many factors that influence the sampling error, such as, extent of mark variation, amount of sample unit and the choice of sampling method, etc.

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