An engineer measures a dependent variable y and independent variables x₁, x₂, and x₃. MINITAB output for the model y = β₀+ β₁x₁+ β₂x₂+ β₃x₃+ ε is presented as follows.

Of the following, which is the best next step in the analysis? Explain your reasoning.

i. Add interaction terms x₁x₂ and x₂x₃ to try to find more variables to put into the model.

ii. Add the interaction term x₁x₃ to try to find another variable to put into the model.

iii. Nothing needs to be done. This model is fine.

iv. Drop x₁ and x₃, and then perform an F test.

v. Drop x₂, and then perform an F test.

vi. Drop the intercept (Constant), since it has the largest P-value.

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The regression equation is Y- 0.367 + 1.61 X1 - 5.51 X2 + 1.27 X3 Predictor Constant X1 X2 X3 Coef 0.3692 SE Coef 0.9231 1.3395 1.4959 1.9760 0.40 0.698 0.254 0.004 0.537 1.21 1.6121 5.5049 3.68 1.2646 0.64