CR design with 2x4 factorial treatments


a) ANOVA
Stat > ANOVA > Two-way...
Responses: yield
Row factor: nitrogen
Column factor: sulphur
Click OK

This model will include an interaction term between the two treatment factors. 
If you want to leave out the interaction term, check "Fit additive model" box. 

You may also "Store residuals" by checking the box, or click on the "Graphs..." button to output residual plots. 

b) Interaction plots
Stat > ANOVA > Interactions Plot...
Responses: yield
Factors: nitrogen sulphur
This will use sulphur as the x-axis variable, and nitrogen as a "by" variable (connected lines are made 
for each level of nitrogen). The two lines are not parallel, indicating an important interaction effect. 

If you use the order
Factor: sulphur nitrogen
Then nitrogen will be the x-axis variable and sulphur a "grouping" variable. 
The four lines cross, indicating an important interaction effect.