NO.PZ2018062016000115
问题如下：
If analyst want to decrease the width of the confidence interval, which of the following statement should be selected.
选项：
A.
increase sample variance
B.
increase number of observations
C.
increase confidence level
解释：
B is correct, if number of observation become larger, sample variance is smaller, the width of confidence interval become smaller.
观察的次数越多，样本方差越小，置信区间的宽度越小。
我理解，公式s/root of n中的n是sample size。现在题目中说的是number of observations变多，sample size只是取样的数，不一定会变大，那么依据公式，confidence interval也不一定会变窄吧？
