Three different brands of magnetron tubes (the key components in microwave ovens) were subjected to stressful testing, and the number of hours each operated without repair was recorded (see the accompanying table). Although these times do not represent typical life lengths, they do indicate how well the tubes can withstand extreme stress. Brand A Brand B Brand C 35 48 71 47 33 31 5 60 140 67 3 58 53 55 42 a Use the F test for a one-way layout (Chapter 13) to test the hypothesis that the mean length of life under stress is the same for the three brands. Use α = .05. What assumptions are necessary for the validity of this procedure? Is there any reason to doubt these assumptions? b Use the Kruskal–Wallis test to determine whether evidence exists to conclude that the brands of magnetron tubes tend to differ in length of life under stress. Test using α = .05
Three different brands of magnetron tubes (the key components in microwave ovens) were subjected to stressful testing, and the number of hours each operated without repair was recorded (see the accompanying table). Although these times do not represent typical life lengths, they do indicate how well the tubes can withstand extreme stress.
Brand A Brand B Brand C
35 48 71
47 33 31
5 60 140
67 3 58
53 55 42
a Use the F test for a one-way layout (Chapter 13) to test the hypothesis that the mean length of life under stress is the same for the three brands. Use α = .05. What assumptions are necessary for the validity of this procedure? Is there any reason to doubt these assumptions?
b Use the Kruskal–Wallis test to determine whether evidence exists to conclude that the brands of magnetron tubes tend to differ in length of life under stress. Test using α = .05
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