NO.PZ2015120604000128
问题如下：
Assume the population is nonnormally distributed, the variance is unknown but the sample size is more than 30. Can we use z-critical value to construct confidence intervals?
选项：
A.
Yes
B.
No
C.
Uncertain
解释：
A is correct.
Under the conditions given in the question, either the t-critical value or the z-critical value is acceptable for constructing confidence intervals.
根据题目中所提供得条件，t 临界值或 z 临界值都可以用于构建置信区间。
（总体）方差已知用z，（总体）方差未知用t，非正态大样本用z或t都可以。
题干是不是不严谨？应该是检验总体均值的时候可以不管总体的分布吧？
