How to Run a 2-Sample T Test in Minitab

When working with data sets in six sigma projects, often there will be a need to compare two groups to each other. A 2-sample T test is a hypothesis test is a hypothesis test to study whether there is a statistically significant difference between the means of two populations. The 2-sample T test runs a comparison of two categories within the same categorical variable, which becomes valuable when trying to answer questions that involve understanding the effects of the addition of a program or change to a sample of subjects.

How to Run a 2-Sample t Test in Minitab

In this example, we will be using a 2-Sample t data file for Minitab. Clicking the previous link will download the file for your use. Once you have the file open in Minitab we will be comparing the price of gasoline between State A and State B. We will use a data set assuming that each data set is normally distributed with equal variances. The hypothesis will be:
Null Hypothesis (H0): μ1 = μ2
Alternative Hypothesis (Ha): μ1 ≠ μ2

Where μ1 is the mean of one population and μ2 is the mean of the other population of our interest.

Step 1: Click Stat → Basic Statistics → 2-Sample t.
2-Sample T Test in Minitab

A new window named “Two-Sample t for the Mean” pops up.

Step 2: Click in the blank box next to “Samples” and the “Gas Price” appears in the list box on the left.

2 Sample-T Test in Minitab

Select “Gas Price” as the “Samples.”

2-Sample T Test

Step 3: Click in the blank box next to “Sample IDs” and the “State” appears in the list box on the left.

Select “State” as the “Sample IDs.”

2-Sample T Test

Step 4: Click options.

Check the box that says “Assume Equal Variances”

2-Sample T Test

Click “OK” to save, and click “OK” again to run the test.

Results of our 2-Sample t Test:

The results for our study of how to run a 2-sample t test in Minitab (when σ1 = σ2) appear automatically in the session window after clicking “OK.” Minitab’s output is below. Take notice of a couple of important bits of information provided by the output. The mean of state A and state B, the number of data points for each state represented by ‘N’ as well as each standard deviation.

2-Sample T Test

The key statistical output provided by Minitab when running a 2-sample t test is the P-Value. Since the p-value of the t-test (assuming equal variance) is 0.665, it’s greater than the alpha level of 0.05. Therefore we fail to reject the null hypothesis which was (H0): μ1 = μ2. Our conclusion in this case is that the means of the two data sets are equal.

 

About Michael Parker

Michael Parker is the President and CEO of the Lean Sigma Corporation, a management consulting firm and online six sigma training, certification and courseware provider. Michael has over 20 years of experience leading and executing lean six sigma programs and projects. As a Fortune 50 senior executive, Michael led oversight of project portfolios as large as 150 concurrent projects exceeding $100 million in annual capital expenditures. Michael has also managed multi-site operations with the accountability of over 250 quality assurance managers, analysts, and consultants. He is an economist by education earning his Bachelor of Science degree from Radford University while also lettering 4 years as an NCAA Division I scholarship athlete. Michael earned his Six Sigma Master Black Belt certification from Bank of America and his Black Belt certification from R.R. Donnelley & Sons.

1 Comment

  1. Mike on February 12, 2019 at 4:47 pm

    Best account I have seen of the 2 sample T test

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