Full model represents the situation where there are differences among some treatment means.
Reduced model represents the situation where there are no differences among any treatment means. See figure 2.2, page 44. The difference between the error sum of squares for the reduced model and the error sum of squares for the full model is the treatment sum of squares . This relationship can be justified by looking at an identity for the deviation of any observation from the grand mean. The sum of squares for all the observations has N statistically independent pieces of information.