An article in the Journal of Pharmaceutical Sciences ( 80 , 971 – 977, 1991) presents data on the observed mole fraction solubility of a solute at a constant temperature, along with x1 = dispersion partial solubility, x2 = dipolar partial solubility, and x3 = hydrogen bonding Hansen partial solubility. The response y is the negative logarithm of the mole fraction solubility.

a. Fit a complete quadratic model to the data.

b. Test for signifi cance of regression, and construct t statistics for each model parameter. Interpret these results.

c. Plot residuals and comment on model adequacy.

d. Use the extra - sum - of - squares method to test the contribution of all second -

order terms to the model.

Observation Number y x1 x2 x3 1 0.22200