Making Boxplot Graphs:
Click on Graphs in the top menu bar of the Data View window.
From the drop down menu select Boxplot...>>>
Select Clustered from the Boxplot dialog box then click
Define. Note: I left the default radio button checked (Summaries for
group cases).
In the Define Clustered Boxplot dialog box move (Plant Growth) into the Variable:
box, Light into the Category Axis: box and Fertilizer into the Define Clusters by: box.
Click on the Options button and in that dialog box check Display groups defined by
missing values then click Continue. Clustered boxplot graphs show an interaction between the light and fertilizer
treatments in their effect on plant growth (N. Clifford and G. Valentine p. 332).