An article in Process Engineering (1992, No. 71, pp. 46€“47) presented a two-factor factorial experiment to investigate the effect of pH and catalyst concentration on product viscosity (cSt). The data are as follows:

(a) Test for main effects and interactions using α = 0.05. What are your conclusions?

(b) Graph the interaction and discuss the information provided by this plot.

(c) Analyze the residuals from this experiment.

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Catalyst Concentration 2.7 178, 186, 179, 188 197, 196, 204, 204 2.5 pH 192, 199, 189, 198 185, 193, 185, 192 5.6 5.9