In Testing the Difference Between Two Population Means Using Two $\bar { x } _ { 1 } - \bar { x } _ { 2 }$

Multiple Choice

In testing the difference between two population means using two independent samples, we use the pooled variance in estimating the standard error of the sampling distribution of the sample mean difference $\bar { x } _ { 1 } - \bar { x } _ { 2 }$ if:

A) the sample sizes are both large.
B) the populations are normal with equal variances.
C) the populations are non-normal with unequal variances.
D) All of these choices are true.