The article "Modeling Resilient Modulus and Temperature Correction for Saudi Roads" (H. Wahhab, I. Asi, and R. Ramadhan, Journal of Materials in Civil Engineering, 2001:298-305) describes a study designed to predict the resilient modulus of pavement from physical properties. The following table presents data for the resilient modulus at 40—¦C in 106 kPa (y), the surface area of the aggregate in m2/kg (x1), and the softening point of the asphalt in —¦C (x2).

The full quadratic model is y = β0 + β1x1 + β2x2 + β3x1x2 + β4x21 + β5x22 + ε. Which submodel of this full model do you believe is most appropriate? Justify your answer by fitting two or more models and comparing the results.

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21921 6667 37478 58977 2 1121 168 9480 68698 32131 60 74 67 70 64 75432 7 57887 363 084