The yield of a chemical process is being studied. The two most important variables are thought to be the pressure and the temperature. Three levels of each factor are selected, and a factorial experiment with two replicates is performed. The yield data follow: Temperature Pressure
200 215 230
150 90.1 90.5 89.9
90.3 90.6 90.1
160 90.5 90.8 90.4
90.7 90.9 90.1
170 90.4 90.7 90.2
90.2 90.6 90.4

(a) Analyze the data and draw conclusions. Show your ANOVA table. Use α = 0.05.
(b) Prepare and show appropriate residual plots and comment on the model’s adequacy.
(c) Under what conditions would you operate this process?