Use the computer output for the radial keratotomy data of Problem 12 in Chapter 8, along with the additional output here, to answer the following questions.
a. Perform the overall F test for the regression of Y on both independent variables. Interpret your result.
b. Perform variables-added-in-order tests for both independent variables, with X1 added first.
c. Perform variables-added-in-order tests for both independent variables, with X2 added first.
d. Provide a table of variables-added-last tests.
e. Which predictors appear to be necessary? Why?