A rubber additive made from cashew nut shells. Refer to the Industrial & Engineering Chemistry Research

(May 2013) study of the use of cardanol as an additive for natural rubber, Exercise 12.24 (p. 700). You analyzed a first-order model for y = grafting efficiency as a function of x1 = initiator concentration (parts per hundred resin), x2 = cardanol concentration (parts per hundred resin), x3 = reaction temperature (degrees Celsius) and x4 = reaction time (hours).

a. Suppose an engineer wants to predict the grafting efficiency of chemical run with initiator concentration set at 5 parts per hundred resin, cardanol concentration at 20 parts per hundred resin, reaction temperature at 30 degrees, and reaction time at 5 hours. Would you recommend using the prediction equation from Exercise 12.24 to obtain this prediction? Explain.

b. Examine the data in the GRAFT file and determine if there is any evidence of multicollinearity. (Note: This result is due to the design of the experiment.)

c. Conduct a complete residual analysis for the model.

Do you recommend any model modifications?