The following MINITAB output presents a multiple regression equation ̂y = b0 + b1x1 + b2x2 + b3x3 + b4x4.

It is desired to drop one of the explanatory variables. Which of the following is the most appropriate action?
i. Drop x3, then see whether R2 increases.
ii. Drop x3, then see whether adjusted R2 increases.
iii. Drop x1, then see whether R2 increases.
iv. Drop x1, then see whether adjusted R2 increases.

The regression equation is Y = 0.742 + 3.58 X1 - 2.18 X2 - 0.818 X3 - 1.58 X4 Predictor Coef StDev T P Constant 0.7424 0.7557 0.9824 0.333 X1 3.5829 1.0602 3.3794 0.002 X2 -2.1772 0.6896 -3.1574 0.003 X3 -0.8177 0.8606 -0.9501 0.349 X4 -1.5840 0.8851 -1.7897 0.082 S = 4.6846 R-sq = 46.0% R-sq (adj) 39.8% = Analysis of Variance Source DF SS MS F _P Regression 4 654.38 163.59 7.4547 0.000 Residual Error 35 768.08 21.945 Total 39 1422.5