Following are data on y = green liquor (g/l) and x paper machine speed (ft/min) from a Kraft paper machine. (The data were read from a graph in an article in the Tappi Journal, March 1986.)
(a) Fit the model Y = β0 + β1x + β2×2 + ϵ using least squares.
(b) Test for significance of regression using α = 0.05. What are your conclusions?
(c) Test the contribution of the quadratic term to the model, over the contribution of the linear term, using a t-test. If
α = 0.05, what conclusion can you draw?
(d) Plot the residuals from the model in part (a) versus . Does the plot reveal any inadequacies?
(e) Construct a normal probability plot of the residuals. Comment on the normality assumption.