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xxxxsdadas · 2020年04月15日

问一道题:NO.PZ2015120604000137 [ CFA I ]

问题如下图:

选项:

A.

B.

C.

解释:

如何理解检验统计量的公式由来?

2 个答案
已采纳答案

星星_品职助教 · 2020年04月16日

get你的问题了。这个公式的解释有一些超出CFA的范畴,教材上也是直接给出了公式。以双尾检验为例简单说一下,不需要掌握。

对于Z检验而言,根据中心极限定理,X bar服从均值为μ,方差为σ2/n的正态分布,所以可以把公式简单理解成一个正态分布的标准化,(X bar-μ)/(σ/√n)~N(0,1),即标准化后的结果服从标准正态分布。这个公式衡量了X bar到μ的距离是几倍的标准差,如果X bar对于总体均值μ的估计是正确的,则这个公式算出来的结果(距离)不应该很大。例如有95%的把握这个距离应该在1.96倍标准差的范围之内。如果超过了1.96,则说明随便抽样一次就发生了小概率事件,这种情况我们认为是不可能发生的,所以原假设错误,需要拒绝。

当总体方差σ未知的时候,由于s是σ的无偏估计量,所以在公式里用s代替,公式变为(X bar-μ)/(σ/√n)~t(n-1),即服从自由度为n-1的t分布。其余逻辑一致。

以上逻辑不需要掌握,考试也不会涉及。只需要根据标准化的思路记忆住公式即可。

星星_品职助教 · 2020年04月15日

同学你好,

计算检验统计量是上课讲过假设检验里的步骤。判断出需要用t检验后,代入课上讲的公式即可

xxxxsdadas · 2020年04月16日

对,我的问题就是那个公式是如何来的?应该如何理解?还是不要求理解只需要死背公式?

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