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rikkisong72 · 2017年07月24日

问一道题：NO.PZ2015121802000021

  1. CFA I

请问这道题为何求的是sample 标准差而不是population的标准差？

问题如下图：

    

选项：

A.

B.

C.

解释：



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源_品职助教 · 2017年07月24日

通常情况下，一个投资的持续期远远超过5年（除非题目明确告诉你目前投资期只有五年），所以5年只是投资期中一个样本时间段。

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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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