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 25-1 design with I = ABCDE was used to investigate the effects of five factors on the color of a chemical product. The factors are A = solvent/reactant, B = catalyst/reactant, C = temperature, D = reactant purity, and E = reactant pH. The responses obtained were as follows:
(a) Prepare a normal probability plot of the effects. Which effects seem active?
(b) Calculate the residuals. 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 25-1 design into a full factorial in the active factors. Comment on the resulting design, and interpret the results.