Consider the regression model fit to the coal and limestone mixture data in Exercise 12-17. Use density as the response. Build regression models for the data using the following techniques:

(a) All possible regressions.

(b) Stepwise regression.

(c) Forward selection.

(d) Backward elimination.

(e) Comment on the models obtained. Which model would you prefer? Why?

Density Dielectric Constant Loss Factor 0.749 2.05 0.016 0.798 2.15 0.02 0.849 2.25 0.022 0.023 0.877 2.3 0.026 0.929 2.4 0.963 2.47 0.028 0.997 2.54 0.031 1.046 2.64 0.034 1.133 0.039 2.85 1.17 2.94 0.042 1.215 3.05 0.045