51. The accompanying data resulted from an experiment to investigate whether yield from a certain chemical process depended either on the formulation of a particular input or on mixer speed.

Speed 60 70 80 189.7 185.1 189.0 1 188.6 179.4 193.0 Formulation 190.1 177.3 191.1 165.1 161.7 163.3 2 165.9 159.8 166.6 167.6 161.6 170.3 A statistical computer package gave SS(Form) 

2253.44, SS(Speed)  230.81, SS(Form*Speed) 

18.58, and SSE  71.87.

a. Does there appear to be interaction between the factors?

b. Does yield appear to depend on either formulation or speed?

c. Calculate estimates of the main effects.

d. Verify that the residuals are 0.23, 0.87, 0.63, 4.50, 1.20, 3.30, 2.03, 1.97, 0.07, 1.10,

0.30, 1.40, 0.67, 1.23, 0.57, 3.43, 0.13, 3.57.

e. Construct a normal plot from the residuals given in part (d). Do the !ijk s appear to be normally distributed?

f. Plot the residuals against the predicted values

(cell means) to see if the population variance appears reasonably constant.