The accompanying MINITAB output resulted from applying both the backward elimination method and the forward selection method to the wood specific gravity data referred to in Exercise 56. For each method, explain what occurred at every iteration of the algorithm.

Response is spgrav on 5 predictors, with N
20 Step 1 2 3 4 Constant 0.4421 0.4384 0.4381 0.5179 sprngfib 0.00011 0.00011 0.00012 T-Value 1.17 1.95 1.98 sumrfib 0.00001 T-Value 0.12

%sprwood 0.00531 0.00526 0.00498 0.00438 T-Value 5.70 6.56 5.96 5.20 spltabs 0.0018 0.0019 T-Value 1.63 1.76 sumltabs 0.0044 0.0044 0.0031 0.0027 T-Value 3.01 3.31 2.63 2.12 S 0.0180 0.0174 0.0185 0.0200 R-Sq 77.05 77.03 72.27 65.50 Step 1 2 Constant 0.7585 0.5179

%sprwood 0.00444 0.00438 T-Value 4.82 5.20 sumltabs 0.0027 T-Value 2.12 S 0.0218 0.0200 R-Sq 56.36 65.50