4.1.2 - Two-Factor Factorial: Greenhouse Example (Minitab)

Minitab 18

Minitab®  – Two-Factor Factorial

For Minitab, we also need to convert the data to a stacked format (Lesson4 2 way Stacked Dataset). Once we do this, we will need to use a different set of commands to generate the ANOVA. We use...

Stat > ANOVA > General Linear Model > Fit the General Linear Model

and get the following dialog box:

Minitab GLM dialog box

Click on the Model box (arrow above), hold down the shift key and highlight both factors.  Then click on the Add box to add the interaction to the model.

Minitab GLM dialog box

Following the ANOVA run, you can generate the mean comparsons by

Stat > ANOVA > General Linear Model > Comparisons

Minitab Comparisons dialog box

Specify the fert*species interaction term in the Terms box for the comparisons, and check the Comparisons box.

This will produce the same ANOVA output as SAS (not shown here), and in addition gives the following table of mean comparison results:

fert species N Mean Grouping
f3 SppB 6 35.1 A
f1 SppB 6 31.6 B
f2 SppB 6 30.0 B
f3 SppA 6 29.2 B C
f1 SppA 6 28.6 B C
f2 SppA 6 25.9 C D
control SppB 6 23.7 D E
control SppB 6 21.0 E

Means that do not share a letter are significantly different.

We can take these out to Excel to make our final graph.