If the populations are normally distributed but the population variances are unknown the z-statistic can be used as the basis for statistical inferences about the difference in two population means using two independent random samples.

Question

Quizplus · Accepted Answer

When the population variances are unknown and the populations are normally distributed, the t-statistic, not the z-statistic, is used for making inferences about the difference between two population means using two independent samples.

If the Populations Are Normally Distributed but the Population Variances