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Hugo(Xie Lanzhi) · 2020年09月04日

问一道题：NO.PZ2015120604000137 [ CFA I ]

  1. CFA I
  2. Quantitative

问题如下：

Ida Lee and his team collect a lot of analysis of statistical data about the car market .According to the data, they come to the conclusion that the mean price of SUV is more than $46,435 in his country. Then they randomly select 64 SUVs whose mean price is $46,760. Assuming the standard deviation of the sample is 1370. Ida Lee conducts a hypothesis test to check their conclusion. At which significant level should Ida Lee reject the null hypothesis?

选项：

A.

0.5%.

B.

5%.

C.

1%.

解释：

B is correct.

If the significant level is 5%, the critical value=1.669<1.8978, Ida Lee should reject the null.

If the significant level is 0.5%, the critical value=2.656>1.8978, Ida Lee will fail to reject the null.

If the significant level is 1%, the critical value=2.387>1.8978, Ida Lee will fail to reject the null.


请问sifnificant level＝5％，对应的critical不应该是1.65吗？这几个significant level对应的critical value怎么和ppt里面的对不上呀？
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2 个答案

星星_品职助教 · 2020年09月23日

@嗨森

n＞30的时候，t分布趋近于z分布，但只是趋近，所以最准确的还是t值。

t的关键值不需要背，考试的时候根据题干条件查表就可以。

星星_品职助教 · 2020年09月04日

同学你好，

1.65是正态分布下的关键值，这道题总体方差未知，需要用的是t检验，所以最准确的方法是需要查表查t的关键值。t关键值要比正态分布对应的关键值略大一些。

但这道题只是判断，所以直接用正态分布下背过的一组值替代t关键值其实也可以。因为两个值差距不大，不影响判断结果。但如果涉及到精确计算就必须要查t表了。

嗨森 · 2020年09月23日

但是这里n=64>30，我记得讲义里有一个类似的老师直接用的z值诶 然后t值的几个需要记一下么？

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