自由度有点记混了，这里为什么不用-1个自由度，毕竟是样本，样本不是都要减一个自由度么
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No.PZ2017092702000108 (选择题)
来源: 原版书
A sample mean is computed from a population with a variance of 2.45. The sample size is 40. The standard error of the sample mean is closest to:
您的回答, 正确答案是: B
A
0.039.
B
正确0.247.
C
0.387.
数据统计(全部)
做对次数: 1870
做错次数: 782
正确率: 70.51%
数据统计(个人)
做对次数: 1
做错次数: 0
正确率: 100.00%
解析
B is correct.
Taking the square root of the known population variance to determine the population standard deviation (σ) results in:
σ = \sqrt{2.45}
2.45
= 1.565
The formula for the standard error of the sample mean (σX), based on a known sample size (n), is: \sigma_X=\frac\sigma{\sqrt n}
σX
=n
σ
Therefore,\sigma_X=\frac{1.565}{\sqrt{40}}=0.247
σX
=40
1.565
=0.247
已知总体方差的平方根来确定总体标准差 (σ) ：
σ = \sqrt{2.45}
2.45
= 1.565
当已知样本量 (n)时，样本均值 (σX) 的标准误：
\sigma_X=\frac\sigma{\sqrt n}
σX
=n
σ
Therefore,\sigma_X=\frac{1.565}{\sqrt{40}}=0.247
σX
=40
1.565
=0.247
