Modeling and Multivariate Methods - SAS

Chapter 3 Fitting Standard Least Squares Models 129
Examples with Statistical Details
There is an intercept plus two effects: one is a nominal main effect using two parameters, and the other is an
interval covariate regressor using one parameter.
Re-run the Snedecor and Cochran Drug.jmp example, but add the x to the model effects as a covariate.
Compared with the main effects model (Drug effect only), the R 2 increases from 22.8% to 67.6%, and the
standard error of the residual reduces from 6.07 to 4.0. As shown in Figure 3.54, the F-test significance
probability for the whole model decreases from 0.03 to less than 0.0001.
Figure 3.54 ANCOVA Drug Results