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。
confidence interval=point estimate ± reliability factor × standard error
如果方差变大, 标准差也会同乡变大, 上面公式里面的减数变大, 所以width变小, 那么A为什么会是错的