统计功效（statistical power ）是指， 在假设检验中， 拒绝原假设后， 接受正确的替换假设的概率。我们知道，在假设检验中有α错误和β错误。α错误是弃真错误， β错误是取伪错误。取伪错误是指， 原假设为假，样本观测值没有落在拒绝域中，从而接受原假设的概率，即在原假设为假的情况下接受原假设的概率。由此可知， 统计功效等于1-β。
目的 ：论述病例 对照研究设计中样本大小与统计功效估计方法。
In this paper we study the size and the power of permutation test and compare them with those of other test methods under small sample size.
而当总贡献率较高时(如70%)，即使PIC值较低，较少的品种数目也可使候选基因的统计功效超过80%。
But, when the contribution was 70%, even if PIC was low, less number of varieties could make more than 80% statistical power.
该方法根据噪声时域特性将其分为结构性噪声和非结构性噪声两类，它们对统计检验功效造成的影响在文中分别进行了讨论。
The fMRI noise is classified into structured and unstructured noise by their temporal characteristics, and their impacts to efficiency of statistical tests are discussed separately.
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