R.D. Snee (“Experimenting with a Large Number of Variables,” in Experiments in Industry: Design, Analysis and Interpretation of Results, by R.D. Snee, LB. Hare, and J.B. Trout, eds., ASQC, 1985) describes an experiment in which a 25-1 design with I = ABCDE was used to investigate the effects of five factors on the color of a chemical product. The factors were A = solvent/reactant, B = catalyst/reactant, C = temperature, D = reactant purity, and E = reactant pH. The results obtained are as follows:
(a) Prepare a normal probability plot of the effects. Which effects seem active? Fit a model using these effects.
(b) Calculate the residuals for the model you fit in part (a). Construct a normal probability plot of the residuals and plot the residuals versus fitted values. Comment on the plots.
(c) If any factors are negligible, collapse the 25-1 design into a full factorial in the active factors. Comment on the resulting design and interpret the results.

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