. R. D. Snee ("Experimenting with a Large Number of Variables," i 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 2-1 design with ] = 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:
e =- 0.63 d = 6.79 a=2.51 ade = 6.47 b =- 2.68 bde = 3.45 abe = 1.66 abd = 5.68 c = 2.06 cde = 5.22 ace = 1.22 acd = 4.38 bce =- 2.09 bed = 4.30 abc = 1.93 abcde = 4.05

(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 resid-
uals and plot the residuals versus the fitted values. Comment on the plots.

(c) If any factors are negligible, col-
lapse the 23" design into a full fac-
torial in the active factors. Comment on the resulting design and interpret the results.