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王思祺 · 2020年08月25日

问一道题:NO.PZ2017092702000156

问题如下:

Using the information in the following table, the sample standard deviation for VWIGX is closest to:

选项:

A.

6.02%

B.

12.04%.

C.

24.54%

解释:

C is correct. The sample variance is defined as sum of the squared deviations from the sample mean divided by the sample size minus one, and the sample standard deviation equals the square root of the sample variance.

The sample variance is thus equals to 6.02. The square root of the sample variance is the sample standard deviation and equals to 24.54%.

A is incorrect because it is the sample variance for VWGIX, not its sample standard deviation.
B is incorrect because it represents the sum of the squared deviations from the mean, not the sample standard deviation.


老师 请问B是怎么算出来的以及计算器STATA得出的20.02是population的方差吗 我只输入了3个数啊 不应该和样本的SX是一样的吗

1 个答案

星星_品职助教 · 2020年08月25日

同学你好,

这道题解法就是用计算器直接解Sx,通过2 nd+7输入三个数字后,用2 nd+8直接找到Sx=24.53 就可以得到答案C选项了。就不需要去考虑干扰项A和B了。这种误导性的选项不需要去考虑协会是怎么设计的。

σx=20.03是总体标准差,但由于题目要求算的是样本标准差Sx,所以也不需要考虑总体标准差σx了。