NO.PZ2022123001000124
问题如下：
Samples of size (n1,n2) are drawn respectively
from two populations (X1,X2) with associated sample means
and standard deviations of 
and (s1, s2) and associated population means
and standard deviations of (μ1, μ2) and (σ1, σ2)
whereσ1≠σ2.
In addition, 
is the sample mean of
X1-X2 with a standard error of sd and a
population mean ofμd0and s2p is a pooled
estimator of the common variance.
The
most appropriate test statistic to determine the equality of the two population
means assuming X1 and X2 are independent and normally
distributed is:
选项：
A.
解释：
The most appropriate test statistic for the difference between two population means (unequal and unknown population variances) is
为什么是s1平方和s2平方，讲义上不是sp平方吗？
