R. D. Snee (“Experimenting with a Large Number of Variables,” in Experiments in Industry: Design, Analysis and Interpretation of Results, by R. D. Snee, L. B. Hare, and J. B. Trout, editors, ASQC, 1985) describes an experiment in which a 2^5-1 design with 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 the fitted values. Comment on the plots.

c. If any factors are negligible, collapse the 2^5-1 design into a full factorial in the active factors. Comment on the resulting design and interpret the results.

1 = ABCDE %3D