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Joyce · 2019年08月27日

问一道题:NO.PZ2015120604000137

问题如下图:

    

选项:

A.

B.

C.

解释:


为什么是查T分布表呢?是因为总体方差未知吗?

1 个答案

星星_品职助教 · 2019年08月27日

同学你好,从题目本身来说,这道题题目中没有说是正态分布,同时总体方差未知,所以用了t分布。

从备考的角度来讲,对于练习题而言,很多题目的出题方式都类似这种,不会明确的告诉你用t还是用z。但用 t分布和z分布的结果几乎是不会有差别,因为t和z的critical value相差很小;就比如这道题,以5%为例,无论是用1.669还是1.645,最后结果都是一样的。

对于真实考试而言,用什么分布或者是用哪个critical value,题干会给出明确的信息,比较典型的一种形式就是告诉单尾5% significant level的critical value就按照1.65来计算。几乎不可能让考生自己去努力从题干中找信息去看到底用哪种分布。

而对于用哪种分布的考察方式,很大可能是直接出一个选择题,题干说方差未知,让考生选择用t还是用z。

加油

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