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Hugo(Xie Lanzhi) · 2020年09月04日

问一道题：NO.PZ2015120604000130 [ CFA I ]

  1. CFA I
  2. Quantitative

问题如下：

We want to use z-statistic to construct confidence interval for a normally distribution. Assume the sample size is 100, sample mean is 15% and the standard deviation of sample is 25%. The significance level is supposed to be 10% , the confidence interval is  :

选项：

A.

- 10.88% to 19.13%.

B.

10.88% to 19.13%.

C.

10.88% to 20.57%.

解释：

B is correct.

In this case, we can know that the Confidence Interval=[Point Estimate +/- (reliability factor)*Standard error]=

x¯±zα/2σn=15%±1.65×25%100=10.88%,19.13%

请问我理解10％不是应该对应双尾，也就是中间部分应该是80％，这么理解有哪里不对吗？
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1 个答案

星星_品职助教 · 2020年09月04日

同学你好，

10%的significance level直接对应就是90%的confidence interval，所以中间部分是90%而不是80%，对应的关键值直接就是要求背过的1.65

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