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Crash Tests The Insurance Institute for Highway Safety regularly tests cars for various safety factors. In one such test, the institute tests the bumpers in 5-mile per hour (mph) crashes. The following data represent the cost of repairs (in dollars) after four different 5-mph crashes on small utility vehicles. The institute blocks by location of crash, and the treatment is car model.

(a) Normal probability plots for each treatment indicate that the requirement of normality is satisfied. Verify that the requirement of equal population variances for each treatment is satisfied. (b) Is there sufficient evidence that the mean cost of repairs is different among the four SUVs at the  level of significance?

(c) If the null hypothesis from part (b) was rejected, use Tukey’s test to determine which pairwise means differ using a familywise error rate of .