Refer to Exercise 8.27.
a. Use a nonparametric procedure to group the suppliers based on their mean deviations. Use an experimentwise error rate of .05.
b. Use the Tukeyâ€™s W procedure to group the suppliers based on their mean deviations. Use an experimentwise error rate of .05.
c. Compare the two sets of groupings. Why is the nonparametric procedure more appropriate in this situation?
Wludyka and Nelson (1997) describe the following study. In the manufacture of soft contact lenses, a monomer is injected into a plastic frame, the monomer is subjected to ultraviolet light and heated (the time, temperate, and light intensity are varied), the frame is removed, and the lens is hydrated. It is thought that temperature can be manipulated to target the power (strength of the lens), so comparing the variability in power is of interest. The data are coded deviations from the target power using monomers from five different suppliers given below.
a. Do the suppliers appear to differ in their levels of variability? Use a Â .05.
b. Is there significant evidence of a difference in the mean deviations for the five suppliers? Use an a Â .05 AOV F test.
c. Apply the Kruskalâ€“Wallis test to evaluate differences in the distributions of the deviations for the five suppliers? Use a Â .05.
d. Suppose a difference in mean deviations of 20 units would have commercial consequences for the manufacturer of the lenses. Does there appear to be a practical difference in the materials from the five suppliers?