Variance Comparison and Analysis

11.8 Students in a business course performed a completely randomized design to test the strength of four brands of trash bags. One-pound weights were placed into a bag, one at a time, until the bag broke. A total of 40 bags, 10 for each brand, were used. The data in the trashbags.xls file gives the weight (in lbs.) required to break the bags.

a. at the .05 level of significance, is there evidence of a difference in the mean strength of the four brands of trash bags?
b. if appropriate, determine which brands differ in mean strength
c. at the .05 level of significance, is there evidence of a difference in the variation in strength among the four brands of trash bags?
d. Which brands should you buy, and which brands should you avoid? Explain.

11.12 Integrated circuits are manufactured on silicon wafers through a process that involves a series of steps. An experiment was carried out to study the effect on the yield of using three methods in the cleansing step (coded to maintain confidentiality). The results (stored in Yield-One Way) are as follows:

New1 New2 Standard
38 29 31
34 35 23
38 34 38
34 20 29
19 35 32
28 37 30

a. At the 0.05 level of significance, is there evidence of a difference in the mean yield among the methods used in the cleansing steps?
b. If appropriate, determine which methods differ in mean yields.
c. At the 0.05 level of significance, is there evidence of a difference in the variation in yields among the different methods?
d. What effect does your result in (c) have on the validity of the results in (a) and (b)?

Data:

KROGER GLAD HEFTY TUFFSTUFF
34 32 33 26
30 42 34 18
40 34 32 20
38 36 40 15
36 32 40 20
30 40 34 20
30 36 36 17
42 43 34 18
36 30 32 19
38 38 34 20