Tests of the Equality of Two Means

Introduction

In this lesson, we'll continue our investigation of hypothesis testing. In this case, we'll focus our attention on a hypothesis test for the difference in two population
means μ₁−μ₂ for
two situations:

• a hypothesis test
  based on the t-distribution, known as the pooled two-sample t-test, for μ₁−μ₂ when
  the (unknown) population variances σ2X and σ2Y are
  equal
• a hypothesis test based on the t-distribution, known as Welch's t-test,
  for μ₁−μ₂ when
  the (unknown) population variances σ2X and Y are
  not equal

Of course, because population variances are generally not known, there is no way of being 100% sure that the population variances are equal or not equal. In order
to be able to determine, therefore, which of the two hypothesis tests we should use, we'll need to make some assumptions about the equality of the variances based on our previous knowledge of the populations we're studying.

• link：
• When Population Variances Are Equal
• When Population Variances Are Not Equal
• Using Minitab