Consider the data of Bethel et al. (1985), discussed in Problem 19 in Chapter 14. Delete the three female subjects, leaving 16 observations. Use FEV1 as the response and AGE, WEIGHT, and HEIGHT as predictors.
a. Use the all possible regressions procedure to suggest a best model.
b. Consider a model with centered AGE, WEIGHT, HEIGHT, and their squares as predictors. Suggest a plausible forward chunkwise strategy for choosing a model, and implement it.
c. Use the all possible regressions procedure for the expanded model to choose a best model.
d. Compare results from parts (a), (b), and (c). What model seems most plausible? How do the data limit your conclusions?