Refer to Exercise 16.10.
a. Write a model that allows a second- order relationship between y and D.
b. How would you test for parallelism of the second- order model? Include the research hypothesis in terms of the model parameters and the form of the F test.
c. What are the degrees of freedom of the F test for parallelism?
d. Indicate how you would perform a test for the effects of treatments adjusted for the covariate.