Solved – How to perform two-sample t-test with Minitab

hypothesis testingminitab

I am trying to do a few tests in Minitab and I don't understand why they are not working out.

First, my data in minitab has several columns: Class Name Gender Height Age, where

  • Class has two values {A,B};
  • Name is the name of the students;
  • Gender is Female or Not female;
  • Age is the age of the student.

My questions I have to answer are as follows:
Is the height of Class A larger than Class B?

My understanding of the question
I should be a 2 sample t-test of the differences of the Height of Class A – Class B

However, every time I try to do a two sample t-test it just compares class with height, which is silly and doesn't workout.

How Do I get Minitab to test Class A's height against Class B's height?

Ps. If I am incorrect in the correct hypothesis testing method, please let me know.

Best Answer

I don't have Minitab so I can't show you the exact syntax or GUI menu actions to perform a t-test for independent samples. However, statistical packages (e.g., R, Stata) generally provide commands to perform a t-test when data are organized as either

  1. two series of measurements, one for each group (usually arranged in two columns);
  2. all individual measurements in one column, described by group levels in another column.

With the example from Wikipedia ("weights of screws that were chosen out of a bucket"), that would mean that scheme 1 looks like: 

+-----+-----+
|A1   |A2   |
+-----+-----+
|30.02|29.89|
+-----+-----+
|29.99|29.93|
+-----+-----+
|30.11|29.72|
+-----+-----+
|29.97|29.98|
+-----+-----+
|30.01|30.02|
+-----+-----+
|29.99|29.98|
+-----+-----+

while for scheme 2 we would arrange data as follows:

+-----+-----+
|30.02|A1   |
+-----+-----+
|29.99|A1   |
+-----+-----+
|30.11|A1   |
+-----+-----+
|29.97|A1   |
+-----+-----+
|30.01|A1   |
+-----+-----+
|29.99|A1   |
+-----+-----+
|29.89|A2   |
+-----+-----+
|29.93|A2   |
+-----+-----+
|29.72|A2   |
+-----+-----+
|29.98|A2   |
+-----+-----+
|30.02|A2   |
+-----+-----+
|29.98|A2   |
+-----+-----+

As explained on this short tutorial on Minitab 2-Sample-t-test, any scheme can be used by filling out the correct option in the 2-Sample-t dialog box. In your case, that means selecting Height as Samples and Class as Subscripts, with Samples arranged in one column. After running your t-test, you may want to check usual assumptions (normality and homogeneity of variance).

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