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。
No.PZ2015120604000128 (选择题)
来源: 品职出题
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?
课上说的是总体方差已知用Z，未知用T。这里虽然方差未知但又可以用Z。请问有没有比较全面的对于所有情况应该用t还是z的梳理？
