The following MINITAB output presents a multiple regression equation ̂y = b0 + b1x1 + b2x2 + b3x3 + b4x4 + b5x5.

It is desired to drop one of the explanatory variables. Which of the following is the most appropriate action?
i. Drop x2, then see whether R2 increases.
ii. Drop x4, then see whether R2 increases.
iii. Drop x4, then see whether adjusted R2 increases.
iv. Drop x2, then see whether adjusted R2 increases.

The regression equation is Y1.38 +1.13 X1 + 4.39 X2 - 1.45 X3 +0.741 X4 +1.71 X5 Predictor Coef StDev T P Constant 1.3774 0.7317 1.8823 0.066 X1 1.1307 0.6932 1.6311 0.110 X2 4.3897 0.6755 6.4987 0.000 X3 -1.4479 0.7978 -1.8149 0.076 X4 0.7414 0.6447 1.1500 0.256 X5 1.7095 0.6266 2.7283 0.009 S = 4.5160 Analysis of Variance R-sq = 63.7% R-sq (adj) 59.6% Source DF SS MS F P Regression 5 1573.38 314.79 15.435 0.000 Residual Error 44 897.35 20.394 Total 49 2471.3