9.2.2.1 - Minitab Express: Independent Means t Test

Here we will use Minitab Express to conduct an independent means t test. Note that Minitab Express uses a more complicated formula for computing the degrees of freedom for this test. To read more about the formulas that Minitab Express uses, see Minitab Express Support.

Within Minitab Express, the procedure for obtaining the test statistic and confidence interval for independent means is identical.

MinitabExpress  – Conducting an Independent Means t Test

Let's compare the mean SAT-Math scores of students who have and have not ever cheated. Both sample sizes are at least 30 so the sampling distribution can be approximated using the \(t\) distribution. 

  1. Open the Minitab Express file:
  2. On a PC: In the menu bar select STATISTICS > Two Samples > t
  3. On a Mac: In the menu bar select Statistics > 2-Sample Inference > t
  4. Double click the variable SATM in the box on the left to insert the variable into the Samples box
  5. Double click the variable Ever Cheat in the box on the left to insert the variable into the Sample IDs box
  6. Click OK

This should result in the following output:

2-Sample t: SATM by Ever Cheat
Method
\(\mu_1\): mean of SATM when Ever Cheat = No
\(\mu_2\): mean of SATM when Ever Cheat = Yes
Difference: \(\mu_1-\mu_2\)

Equal variances are not assumed for this analysis.

Descriptive Statistics: SATM
Ever Cheat N Mean StDev SE Mean
No 163 603.988 86.893 6.806
Yes 53 583.68 79.18 10.88
Estimation for Difference
Difference 95% CI for Difference
20.31 (-5.16, 45.78)
Test
Null hypothesis \(H_0\): \(\mu_1-\mu_2=0\)
Alternative hypothesis \(H_1\): \(\mu_1-\mu_2\neq0\)
T-Value DF P-Value
1.58 95 0.1168
Video Walkthrough

Select your operating system below to see a step-by-step guide for this example.

The result of our two independent means t test is \(t(95) = 1.58, p = 0.1168\). Our p-value is greater than the standard alpha level of 0.05 so we fail to reject the null hypothesis. There is not evidence to state that the mean SAT-Math scores of students who have and have not ever cheated are different. 

Note that we could also interpret the confidence interval in this output. We are 95% confident that the mean difference in the population is between -5.16 and 45.78.

The example above uses a dataset. The following examples show how you can conduct this type of test using summarized data.