The following data resulted from an experiment to assess the potential of unburnt collie...

The following data resulted from an experiment to assess the potential of unburnt colliery spoil as a medium for plant growth. The variables are x = acid extractable cations and y = exchangeable acidity/total cation exchange capacity (“Exchangeable Acidity in Unburnt Colliery Spoil,” Nature, 1969: 161):

Standardizing the independent variable x to obtain and fitting the regression function yielded the accompanying computer output.

a. Estimate .

b. Compute the value of the coefficient of multiple determination. (See Exercise 28(c).)

c. What is the estimated regression function using the unstandardized variable x?

d. What is the estimated standard deviation of computed in part (c)?

e. Carry out a test using the standardized estimates to decide whether the quadratic term should be retained in the model. Repeat using the unstandardized estimates. Do your conclusions differ?

Reference exerecise 28

The viscosity (y) of an oil was measured by a cone and plate viscometer at six different cone speeds (x). It was assumed that a quadratic regression model was appropriate, and the n = 6 estimated regression function resulting from the observations was