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kevinzhu · 2019年11月25日

问一道题：NO.PZ2015121802000021 [ CFA I ]

  1. CFA I
  2. Portfolio

问题如下图：

选项：

A.

B.

C.

解释：

Sample variance = 78.8/(5 - 1) = 19.7 为什么要除以n-1?
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星星_品职助教 · 2019年11月26日

同学你好，

这里要求的是“样本”的方差。回忆一下数量里的内容，总体方差分母除以的是n，而样本除以的是n-1，这么做的目的是因为只有除以n-1才是一个最好的估计量。

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NO.PZ2015121802000021问题如下Calculate the stanrviation of annureturns on investment baseon the following chart:A.1.2%.B.4.44%.C.19.7%.B is correct.Meannureturn = (4% - 3% - 4% + 3% + 6%) / 5 = 1.2%Squareviations from the mean: 4%-1.2%=2.8% （2.8%）2= 7.84-3% -1.2% = -4.2% （-4.2%）2 = 17.64-4% -1.2% = -5.2% （-5.2%）2 = 27.043% -1.2% =1.8% （1.8%）2= 3.246% -1.2% = 4.8% （4.8%） 2= 23.04Sum of squareviations = 7.84 + 17.64 + 27.04 + 3.24+ 23.04 = 78.8Sample varian= 78.8/(5 - 1) = 19.7Sample stanrviation = 19.71/2= 4.44%什么时候要除n-1 什么时候除n

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