When testing the difference between two population means, the variances are pooled when
A) the population standard deviations are known and equal.
B) the population means are known.
C) the population standard deviations are assumed unequal and unknown.
D) the population standard deviations are assumed equal but unknown.

Question

Quizplus · Accepted Answer

When testing the difference between two population means, the variances are pooled when the population standard deviations are assumed equal but unknown. In this case, we estimate the common population variance from the sample variances and use it to calculate the test statistic. This approach is more efficient than using separate variances for each population when they are assumed to be equal.

When Testing the Difference Between Two Population Means, the Variances