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哈桑哥 · 2017年02月21日

问一道题：NO.PZ2015121802000021 [ CFA I ]

  1. CFA I

问题如下图：

    

选项：

A.

B.

C.

为什么这个地方答案要除以n-1？

题目并没有说是样本标准差啊。。。

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maggie_品职助教 · 2017年02月21日

只要题目没给出是总体，我们一般认为都是样本。因为我们并不知这项投资的总投资期和计算回报率的频率，仅选用其中5年的年数据，明显就是个样本。

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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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