The accompanying data resulted from a study of the relationship between y = brightness of finished paper and the independent variables x1 = hydrogen peroxide (% by weight), x2 = sodium hydroxide (% by weight), x3 = silicate (% by weight), and x4 = process temperature (“Advantages of CE-HDP Bleaching for High Brightness Kraft Pulp Production,” TAPPI [1964]: 107A–173A).
a. Find the estimated regression equation for the model that includes all independent variables, all quadratic terms, and all interaction terms.
b. Using a .05 significance level, perform the model utility test.
c. Interpret the values of the following quantities: SSResid, R2 , and se.