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从两阶群团抽样的概念入手，根据两阶群团抽样当群团之间不存在差异成分（Ｓβ２＝０）时与系统抽样或简单随机抽样具有相同的抽样效率的性质，定义了误差扩大因子，提出了效率系数的概念，并推导出了效率系数等于１的临界状态的相关系数ｒ＊的表达式，为群团抽样设计和效率评估提供了重要依据。此外，还对群团抽样估计效率与群内样地间距的关系进行了较深入的研究，并用实例进行了说明。最后，对两阶群团抽样在森林调查中的综合效率评价也进行了讨论。
Starting from the concept of two-order group sampling, the error amplification is defined according to the same sampling efficiency as that of the system sampling or the simple random sampling when there is no difference component (Sβ2 = 0) between the two groups. Factor, the concept of efficiency coefficient is proposed and the expression of the correlation coefficient r * of the critical state with efficiency coefficient equal to 1 is derived, which provides an important basis for cluster sampling design and efficiency evaluation. In addition, the relationship between the estimated efficiency of cluster sampling and the distance between the samples in the cluster is also studied in detail, and examples are given. Finally, the comprehensive efficiency evaluation of two-group cluster sampling in forest surveys is also discussed.