题目
A pooled estimator is used when testing a hypothesis concerning the:
选项
A.equality of the variances of two normally distributed populations.
B.difference between the means of two at least approximately normally distributed populations with unknown but assumed equal variances.
C.difference between the means of two at least approximately normally distributed populations with unknown and assumed unequal variances.
答案
B
解析
： B is correct. The assumption that the variances are equal allows for the combining of both samples to obtain a pooled estimate of the common variance. ： B正确。 方差相等的假设允许两个样本的组合以获得共同方差的综合估计量。 补充如图信息，Sp的平方就是pooled estimator（综合估计量），是在： 1.检验两个正太分布的总体均值是否相等 2.其中总体方差未知但是假定相等 这两个条件下使用的