220.127.116.11 - 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. Above, we found that the sample standard deviations are similar, so we will assume equal variances.
- Open the Minitab Express file:
- On a PC: In the menu bar select STATISTICS > Two Samples > t
- On a Mac: In the menu bar select Statistics > 2-Sample Inference > t
- Double click the variable SATM in the box on the left to insert the variable into the Samples box
- Double click the variable Ever Cheat in the box on the left to insert the variable into the Sample IDs box
- Click OK
This should result in the following output:
|\(\mu_1\): mean of SATM when Ever Cheat = No|
|\(\mu_2\): mean of SATM when Ever Cheat = Yes|
Equal variances are not assumed for this analysis.
|Ever Cheat||N||Mean||StDev||SE Mean|
|Difference||95% CI for Difference|
|Null hypothesis||\(H_0\): \(\mu_1-\mu_2=0\)|
|Alternative hypothesis||\(H_1\): \(\mu_1-\mu_2\neq0\)|
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.