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==== 一、标准误（standard error of Xbar） ====
标准误指的是样本均值分布的标准差，用于衡量样本均值分布的变异性，即：

The standard error refers to the standard deviation of the distribution of sample means, used to measure the variability of the sample mean distribution.
{{ ::标准误.jpg?nolink&200 |}}

==== 二、样本均值分布的概率（The probability distribution of sample means） ====
我们同样可以用z分数来描述选取的一个样本在样本均值分布中的位置。但是这里使用的计算z分数的公式与之前有所不同：

We can also use z-scores to describe the position of a selected sample within the distribution of sample means. However, the formula used to calculate the z-score here is different from before:
{{ ::计算z分数.jpg?nolink&150 |}}
和之前计算z分数时不同的是，这里我们把单个分数替换为样本均值，把之前使用的标准差替换为前面提到的标准误，而所对应的分布为样本均值分布。每一个样本均值都有一个所对应的z分数，我们可以通过已知的z分数求出样本均值的概率。

Different from calculating z-scores previously, here we replace individual scores with sample means, and the standard deviation previously used is replaced by the standard error mentioned earlier, with the corresponding distribution being the distribution of sample means. Each sample mean has a corresponding z-score, and we can determine the probability of the sample mean by known z-scores.