NO.PZ2022062760000017
问题如下:
Using the returns of the prior 12 months, an analyst estimates the mean monthly return of stock XYZ to be -0.75% with a standard error of 2.70%.
Using the t-table above, which of the following is the 95% confidence interval for the mean return?
选项:
A.
-6.69% and 5.19%
B.
-6.63% and 5.15%
C.
-5.60% and 4.10%
D.
-5.56% and 4.06%
解释:
中文解析:
区间=mean+z值*σ
mean=-0.75%
σ=2.7%
z值的查找:自由度=12-1=11,双尾5%,单尾2.5%
z值=2.201
区间=-0.75% - 2.201*2.70% and -0.75% + 2.201*2.70%
The confidence interval is equal to the mean monthly return plus or minus the t-statistic times the standard error. To get the proper t-statistic, the 0.025 column must be used since this is a two-tailed interval. Since the mean return is being estimated using the sample observations, the appropriate degrees of freedom to use is equal to the number of sample observations minus 1, which is 11. Therefore, the proper statistic to use from the t-distribution is 2.201. The 95% confidence interval is between -0.75% - 2.201*2.70% and -0.75% + 2.201*2.70%.
什么时候标准误可以直接作为标准差使用,什么时候用标准误除以根号n计算出标准差?