SECTION 8.3195(d)0204060050100150200250R13R14The correlation coefficient betweenR31andR41is 0.997.(e)R31andR41are nearly collinear.(f) The cubic model is best. The quadratic is inappropriate because the residual plot exhibits a pattern. The residualplots for both the cubic and quartic models look good, however, there is no reason to includeR41in the modelsince it merely confounds the effect ofR31.Section 8.31. (a) False. There are usually several models that are about equally good.(b) True.(c) False. Model selection methods can suggest models that fit the data well.
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